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JEE • MATHEMATICS • MATRICES

Matrices practice · Medium

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121 Medium
121 of 408
Analyzing +4 | -1
If Δ1=∣xsin⁡θcos⁡θ−sin⁡θ−x1cos⁡θ1x∣\Delta_1=\left|\begin{array}{ccc}x & \sin \theta & \cos \theta \\ -\sin \theta & -x & 1 \\ \cos \theta & 1 & x\end{array}\right| and

Δ2=∣xsin⁡2θcos⁡2θ−sin⁡2θ−x1cos⁡2θ1x∣,x≠0\Delta_2=\left|\begin{array}{ccc}x & \sin 2 \theta & \cos 2 \theta \\ -\sin 2 \theta & -x & 1 \\ \cos 2 \theta & 1 & x\end{array}\right|, x \neq 0
then for all θ∈(0,π2)\theta \in\left(0, \frac{\pi}{2}\right) :
View answer and explanation
Correct option: D
Δ1+Δ2=−2x3\Delta_1+\Delta_2=-2 x^3
Option D (Δ1+Δ2=−2x3\Delta_1+\Delta_2=-2 x^3) is correct because both determinants simplify to −x3-x^3, and their sum is −2x3-2x^3.
122 Medium
122 of 408
Application +4 | -1
The value of Δ=∣aa+ba+2ba+2baa+ba+ba+2ba∣\Delta = \left| {\begin{array}{cccccccccccccccccccc} a&{a + b}&{a + 2b}\\ {a + 2b}&a&{a + b}\\ {a + b}&{a + 2b}&a \end{array}} \right| is equal to
View answer and explanation
Correct option: B
9b2(a+b)9{b^2}\left( {a + b} \right)
Option B (9b2(a+b)9{b^2}(a + b)) is correct because after applying column operations and simplifying the determinant, the result is 9b2(a+b)9{b^2}(a + b).
123 Medium
123 of 408
Application +4 | -1
Let a,b,c,a,b,c, be positive and not all equal, the value of the Determinant ∣abcbcacab∣\left| {\begin{array}{cccccccccccccccccccc} a&b&c\\ b&c&a\\ c&a&b \end{array}} \right| is
View answer and explanation
Correct option: B
Negative
Option B (Negative) is correct because the determinant simplifies to a negative expression given the conditions on a, b, and c.
124 Medium
124 of 408
Understanding +4 | -1
If l1,m1,n1;l2,m2,n2l_1, m_1, n_1 ; l_2, m_2, n_2 and l3,m3,n3l_3, m_3, n_3 are direction cosines of three mutually perpendicular lines then, the value of ∣l1m1n1l2m2n2l3m3n3∣,\left|\begin{array}{lll}l_1 & m_1 & n_1 \\ l_2 & m_2 & n_2 \\ l_3 & m_3 & n_3\end{array}\right|, is
View answer and explanation
Correct option: B
±1\pm 1
Option B (±1\pm 1) is correct because the determinant of the direction cosines of three mutually perpendicular lines is either 1 or -1.
125 Medium
125 of 408
Analyzing +4 | -1
The number of triplets satisfying the equation ∣x3+1x2yx2zxy2y3+1y2zxz2yz2z3+1∣=11\left| {\begin{array}{cccccccccccccccccccc} {{x^3} + 1}&{{x^2}y}&{{x^2}z} \\ {x{y^2}}&{{y^3} + 1}&{{y^2}z} \\ {x{z^2}}&{y{z^2}}&{{z^3} + 1} \end{array}} \right| = 11 where x, y, zx, \, y, \, z are positive integers
View answer and explanation
Correct option: B
3
Option B (3) is correct because there are three triplets (2,1,1), (1,2,1), and (1,1,2) that satisfy the equation x3+y3+z3=10.
126 Medium
126 of 408
Understanding +4 | -1
From the matrix equation AB=ACAB = AC we can conclude B=CB = C provided that
View answer and explanation
Correct option: B
AA is non-singular
Option B (AA is non-singular) is correct because if AA is non-singular, it has an inverse, allowing us to multiply both sides of the equation AB=ACAB = AC by A−1A^{-1} to get B=CB = C.
127 Medium
127 of 408
Analyzing +4 | -1
If A,BA,B and CC are the angles of a triangle and ∣1111+sin⁡A1+sin⁡Bsin⁡Csin⁡A+sin⁡2Asin⁡B+sin⁡2Bsin⁡C+sin⁡2C∣=0\left| {\begin{array}{cccccccccccccccccccc} 1&1&1\\ {1 + \sin A}&{1 + \sin B}&{\sin C}\\ {\sin A + {{\sin }^2}A}&{\sin B + {{\sin }^2}B}&{\sin C + {{\sin }^2}C} \end{array}} \right| = 0 then the triangle must be
View answer and explanation
Correct option: B
Isosceles
The triangle must be isosceles because the determinant simplifies to a product of differences of sines of angles, which equals zero only when at least two angles have equal sines.
128 Medium
128 of 408
Analyzing +4 | -1
If x,y,zx, y, z are unequal and ∣x3(x+a)3(x−a)3y3(y−a)3(y−a)3z3(z+a)3(z−a)3∣=0\left|\begin{array}{ccc} x^3 & (x+a)^3 & (x-a)^3 \\ y^3 & (y-a)^3 & (y-a)^3 \\ z^3 & (z+a)^3 & (z-a)^3 \end{array}\right|=0 the the value of a2(x+y+z)a^2(x+y+z)
View answer and explanation
Correct option: B
3xyz3 x y z
Option B is correct because after applying column operations and simplifying the determinant, the equation leads to a2(x+y+z)=3xyza^2(x+y+z) = 3xyz.
129 Medium
129 of 408
Analyzing +4 | -1
If A=[21−1352161]A=\left[\begin{array}{rrr}2 & 1 & -1 \\ 3 & 5 & 2 \\ 1 & 6 & 1\end{array}\right], then tr⁡(Aadj⁡(adj⁡A)\operatorname{tr}(\operatorname{Aadj}(\operatorname{adj} \mathrm{A})) is equal to (where tr⁡(P)\operatorname{tr}(\mathrm{P}) denotes the trace of the matrix P i.e the sum of all the diagonal elements of the matrix P and adj (P) denotes the adjoint of matrix P)
View answer and explanation
Correct option: D
−1624-1624
Option D (-1624) is correct because it is the trace of the matrix Aadj(adj A) which can be simplified using properties of adjoint and determinant.
130 Medium
130 of 408
Analyzing +4 | -1
If α,β,γ∈R\alpha ,\beta ,\gamma \in R, then the determinant Δ=∣(eiα+e−iα)2(eiα−e−iα)24(eiβ+e−iβ)2(eiβ−e−iβ)24(eiγ+e−iγ)2(eiγ−e−iγ)24∣\Delta = \left| {\begin{array}{cccccccccccccccccccc} {{{\left( {{e^{i\alpha }} + {e^{ - i\alpha }}} \right)}^2}}&{{{\left( {{e^{i\alpha }} - {e^{ - i\alpha }}} \right)}^2}}&4\\ {{{\left( {{e^{i\beta }} + {e^{ - i\beta }}} \right)}^2}}&{{{\left( {{e^{i\beta }} - {e^{ - i\beta }}} \right)}^2}}&4\\ {{{\left( {{e^{i\gamma }} + {e^{ - i\gamma }}} \right)}^2}}&{{{\left( {{e^{i\gamma }} - {e^{ - i\gamma }}} \right)}^2}}&4 \end{array}} \right| is
View answer and explanation
Correct option: A
Independent of α,β\alpha ,\beta and γ\gamma
The correct answer is A (Independent of α,β\alpha ,\beta and γ\gamma) because the determinant simplifies to 0, which is independent of the variables.
131 Medium
131 of 408
Analyzing +4 | -1
Let A,B,CA, B, C be 3×33 \times 3 matrices such that AA is symmetric and BB and CC are skew-symmetric.

Consider the statements

(S1) A13B26−B26A13A^{13} B^{26}-B^{26} A^{13} is symmetric

(S2) A26C13−C13A26A^{26} C^{13}-C^{13} A^{26} is symmetric
Then,
View answer and explanation
Correct option: B
Only S2 is true
Option B (Only S2 is true) is correct because only A26C13−C13A26A^{26} C^{13}-C^{13} A^{26} is symmetric, while A13B26−B26A13A^{13} B^{26}-B^{26} A^{13} is skew-symmetric.
132 Medium
132 of 408
Understanding +4 | -1
Consider the system of equations a1x+b1y+c1z=0a_1 x+b_1 y+c_1 z=0, a2x+b2y+c2z=0,a3x+b3y+c3z=0a_2 x+b_2 y+c_2 z=0, a_3 x+b_3 y+c_3 z=0. If ∣a1b1c1a2b2c2a3c3c3∣=0\left|\begin{array}{lll}a_1 & b_1 & c_1 \\ a_2 & b_2 & c_2 \\ a_3 & c_3 & c_3\end{array}\right|=0, then the system has
View answer and explanation
Correct option: A
More than 2 solutions
Option A (More than 2 solutions) is correct because when the determinant of the coefficient matrix is zero, the system has non-trivial solutions, implying more than one solution.
133 Medium
133 of 408
Analyzing +4 | -1
Suppose p,q,r≠0p, q, r \neq 0 and system of equations
(p+a)x+by+cz=0ax+(q+b)y+cz=0ax+by+(r+c)z=0\begin{array}{l} (p+a) x+b y+c z=0 \\ a x+(q+b) y+c z=0 \\ a x+b y+(r+c) z=0 \end{array}

has a non-trivial solution, then value of ap+bq+cr\frac{a}{p}+\frac{b}{q}+\frac{c}{r} is
View answer and explanation
Correct option: A
-1
Option A (-1) is correct because the determinant of the coefficient matrix must be zero for a non-trivial solution, leading to the equation a/p + b/q + c/r = -1.
134 Medium
134 of 408
Analyzing +4 | -1
If a1,a2,a3a_1, a_2, a_3, ana_n, are in G. P., then the determinant
Δ=∣log⁡anlog⁡an+1log⁡an+2log⁡an+3log⁡an+4log⁡an+5log⁡an+6log⁡an+7log⁡an+8∣\Delta=\left|\begin{array}{ccc} \log a_n & \log a_{n+1} & \log a_{n+2} \\ \log a_{n+3} & \log a_{n+4} & \log a_{n+5} \\ \log a_{n+6} & \log a_{n+7} & \log a_{n+8} \end{array}\right|
is equal to
View answer and explanation
Correct option: B
0
The correct answer is 0 because the rows of the determinant become linearly dependent when the terms are in a G.P.
135 Medium
135 of 408
Application +4 | -1
Let P=[3212−1232],A=[1101]P=\left[\begin{array}{cc}\frac{\sqrt{3}}{2} & \frac{1}{2} \\ -\frac{1}{2} & \frac{\sqrt{3}}{2}\end{array}\right], A=\left[\begin{array}{ll}1 & 1 \\ 0 & 1\end{array}\right] and Q=PAPTQ=P A P^{T}. If PTP^{T} Q2007P=[abcd]Q^{2007} P=\left[\begin{array}{ll}a & b \\ c & d\end{array}\right], then 2a+b−3c−4d2 a+b-3 c-4 d equal to
View answer and explanation
Correct option: B
2005
The correct answer is 2005 because after simplifying the matrix operations and using the properties of matrix exponentiation, the final expression evaluates to 2005.
136 Medium
136 of 408
Application +4 | -1
A root of the equation ∣3−x−63−63−x333−6−x∣=0,\left| {\begin{array}{cccccccccccccccccccc} {3 - x}&{ - 6}&3\\ { - 6}&{3 - x}&3\\ 3&3&{ - 6 - x} \end{array}} \right| = 0, is
View answer and explanation
Correct option: C
0
Option C (0) is correct because x=0 is a root of the equation after applying column and row operations and simplifying the determinant.
137 Medium
137 of 408
Application +4 | -1
If A,BA, B and CC are the angles of a non-right angled triangle ABCA B C, then the value of ∣tan⁡A111tan⁡B111tan⁡C∣\left|\begin{array}{ccc}\tan \mathrm{A} & 1 & 1 \\ 1 & \tan \mathrm{B} & 1 \\ 1 & 1 & \tan \mathrm{C}\end{array}\right| is equal to
View answer and explanation
Correct option: B
2
Option B (2) is correct because using the trigonometric identity tan⁡A+tan⁡B+tan⁡C=tan⁡Atan⁡Btan⁡C\tan A + \tan B + \tan C = \tan A \tan B \tan C for a non-right angled triangle, the determinant simplifies to 2.
138 Medium
138 of 408
Application +4 | -1
Let A=(12−2−5)A=\left(\begin{array}{cc}1 & 2 \\ -2 & -5\end{array}\right). Let α,β∈R\alpha, \beta \in \mathbb{R} be such that αA2+βA=2I\alpha A^2+\beta A=2 I. Then α+β\alpha+\beta is equal to
View answer and explanation
Correct option: D
10
Option D (10) is correct because the characteristic equation of the matrix A can be used to find the relationship between A2 and A, which leads to the value of α + β.
139 Medium
139 of 408
Application +4 | -1
If A=[1111]A=\left[\begin{array}{ll}1 & 1 \\ 1 & 1\end{array}\right] and det⁡(An−I)=1−λn,n∈N,\operatorname{det}\left(A^n-I\right)=1-\lambda^n, n \in N, then the value of λ,\lambda, is
View answer and explanation
Correct option: B
2
Option B (2) is correct because after calculating AnA^n and the determinant of An−IA^n - I, we find that λ\lambda equals 2.
140 Medium
140 of 408
Analyzing +4 | -1
If a1b1c1,a2b2c2a_1 b_1 c_1, a_2 b_2 c_2 and a3b3c3a_3 b_3 c_3 are three-digit numbers, each of which is divisible by a non zero integer k{k}, then Δ=∣a1b1c1a2b2c2a3b3c3∣\Delta=\left|\begin{array}{lll}a_1 & b_1 & c_1 \\ a_2 & b_2 & c_2 \\ a_3 & b_3 & c_3\end{array}\right| is always
View answer and explanation
Correct option: A
Divisible by kk
Option A (Divisible by k) is correct because the determinant can be expressed as k times another determinant with integer elements.
141 Medium
141 of 408
Application +4 | -1
The value of a,b,ca, b, c when [02bcab−ca−bc]\left[\begin{array}{ccc}0 & 2 b & c \\ a & b & -c \\ a & -b & c\end{array}\right] orthogonal, are
View answer and explanation
Correct option: C
±12,±16,±13\pm \frac{1}{\sqrt{2}}, \pm \frac{1}{\sqrt{6}}, \pm \frac{1}{\sqrt{3}}
Option C (±12,±16,±13\pm \frac{{1}}{{\sqrt{{2}}}}, \pm \frac{{1}}{{\sqrt{{6}}}}, \pm \frac{{1}}{{\sqrt{{3}}}}) is correct because the given matrix is orthogonal, implying that A*A^T = I, which leads to the specified values for a, b, and c after solving the resulting equations.
142 Medium
142 of 408
Application +4 | -1
If A=[4325]{A}=\left[\begin{array}{ll}4 & 3 \\ 2 & 5\end{array}\right] and A2−mA+nI=0{A}^2-m {A}+n {I}=0, then
View answer and explanation
Correct option: C
m=9,n=14m=9, n=14
Option C (m=9,n=14m=9, n=14) is correct because substituting these values into the equation A2−mA+nI=0A^2 - mA + nI = 0 satisfies the equation.
143 Medium
143 of 408
Application +4 | -1
Let
A=13[12221−2x2y]A=\frac{1}{3}\left[\begin{array}{rrr} 1 & 2 & 2 \\ 2 & 1 & -2 \\ x & 2 & y \end{array}\right]

If AAT=I3A A^{\mathrm{T}}=I_3, then
View answer and explanation
Correct option: C
x=−2,y=−1x=-2, y=-1
Option C is correct. By using the property AA^T = I, we can set up equations and solve for x and y, which results in x = -2 and y = -1.
144 Medium
144 of 408
Analyzing +4 | -1
The number of 3×33 \times 3 matrices AA whose entries are either 0 or 1 and for which the system A[xyz]=[100]A\left[ {\begin{array}{cccccccccccccccccccc} x\\ y\\ z \end{array}} \right] = \left[ {\begin{array}{cccccccccccccccccccc} 1\\ 0\\ 0 \end{array}} \right] has exactly two distinct solutions, is
View answer and explanation
Correct option: A
0
Option A (0) is correct because a system of linear equations cannot have exactly two distinct solutions; it can have either zero, one, or infinitely many solutions.
145 Medium
145 of 408
Analyzing +4 | -1
The number of values of kk for which the system of linear equations, (k+2)x+10y=k,kx+(k+3)y=k−1(k+2) x+10 y=k, k x+(k+3) y=k-1 has no solution, is
View answer and explanation
Correct option: C
2
Option D (1) is correct because only one value of k (k=3) results in the system having no solution after checking for consistency.
146 Medium
146 of 408
Analyzing +4 | -1
If a,b,ca, b, c are sides of a scalene triangle, then the value of ∣abcbcacab∣\left|\begin{array}{lll}a & b & c \\ b & c & a \\ c & a & b\end{array}\right| is :
View answer and explanation
Correct option: B
negative
The correct answer is negative because the determinant of the given form for a scalene triangle is always negative.
147 Medium
147 of 408
Analyzing +4 | -1
If the value of the determinant ∣a111b111c∣\left| {\begin{array}{cccccccccccccccccccc} a&1&1\\ 1&b&1\\ 1&1&c \end{array}} \right| is positive, then
View answer and explanation
Correct option: B
abc>−8abc > - 8
Option B (abc>−8abc > -8) is correct because by using AM > GM inequality and simplifying the determinant condition, we arrive at abc>−8abc > -8.
148 Medium
148 of 408
Application +4 | -1
For non-singular square matrices A,  BA,\;B and CC of same order, (AB−1C)−1{\left( {A{B^{ - 1}}C} \right)^{ - 1}} is equal to
View answer and explanation
Correct option: D
C−1BA−1{C^{ - 1}}B{A^{ - 1}}
Option D is correct because applying the inverse properties to the expression results in C⁻¹BA⁻¹.
149 Medium
149 of 408
Analyzing +4 | -1
If the system of equations
x+y+z=5x + y + z = 5
x+2y+3z=9x + 2y + 3z = 9
x+3y+αz=β  x + 3y + \alpha z = \beta \,\,
has infinitely many solutions, then β−α\beta - \alpha equals
View answer and explanation
Correct option: A
8
Option A (8) is correct because when the system has infinitely many solutions, the determinant of the coefficient matrix and related determinants must be zero, leading to β−α=8\beta - \alpha = 8.
150 Medium
150 of 408
Application +4 | -1
If A=[cos⁡θ−sin⁡θsin⁡θcos⁡θ]A=\left[\begin{array}{cc}\cos \theta & -\sin \theta \\ \sin \theta & \cos \theta\end{array}\right], then the matrix A−50A^{-50} when θ=π12\theta=\frac{\pi}{12}, is equal to
View answer and explanation
Correct option: A
[3/21/2−1/23/2]\left[\begin{array}{cc}\sqrt{3} / 2 & 1 / 2 \\ -1 / 2 & \sqrt{3} / 2\end{array}\right]
Option A ([3/21/2−1/23/2]\left[\begin{array}{cc}\sqrt{3} / 2 & 1 / 2 \\ -1 / 2 & \sqrt{3} / 2\end{array}\right]) is correct because it represents the matrix A raised to the power of -50 when theta is pi/12, obtained by using the properties of rotation matrices.
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