JEE Mathematics · 271 questions · Page 17 of 28 · Click an option or "Show Solution" to reveal answer
Q161
Let the system of equations x+2y+3z=5,2x+3y+z=9,4x+3y+λz=μ have infinite number of solutions. Then λ+2μ is equal to :
A22
B17
C15
D28
Correct Answer
Option B
Solution
x+2y+3z=52x+3y+z=94x+3y+λz=μ
For infinite following Δ=Δ1=Δ2=Δ3=0Δ=12423331λ=0⇒λ=−13Δ1=59μ23331−13=0⇒μ=15Δ2=124591531−13=0
Δ3=1242335915=0
For λ=−13,μ=15 system of equation has infinite solution hence λ+2μ=17
Q162
If A=[2−112],B=[1101],C=ABAT and X=ATC2A, then detX is equal to :
A243
B729
C27
D891
Correct Answer
Option B
Solution
The solution involves understanding matrix operations and properties such as multiplication, transpose, and determinant.
Given A, B, and that C=ABAT, and X=ATC2A, we find detX as follows: First, we express ∣C∣, the determinant of C, in terms of the determinants of A and B, using the property that ∣ABC∣=∣A∣⋅∣B∣⋅∣C∣: ∣C∣=∣ABAT∣=∣A∣⋅∣B∣⋅∣AT∣=∣A∣2⋅∣B∣since ∣AT∣=∣A∣. Next, we find ∣X∣, using the property ∣ABC∣=∣A∣⋅∣B∣⋅∣C∣ and substituting ∣C∣: ∣X∣=∣ATC2A∣=∣AT∣⋅∣C∣2⋅∣A∣=∣A∣2⋅∣C∣2. Substituting the expression for ∣C∣ obtained earlier: ∣X∣=∣A∣2⋅(∣A∣2⋅∣B∣)2=(∣A∣3⋅∣B∣)2. The determinants of A and B are calculated as:
∣A∣=2−112=2+1=3
∣B∣=1101=1
Finally, substituting these values into our expression for ∣X∣: ∣X∣=(33⋅1)2=729. Therefore, detX=729.
Q163
If the system of equations 2x+3y−z=5x+αy+3z=−43x−y+βz=7 has infinitely many solutions, then 13αβ is equal to :
A1110
B1120
C1210
D1220
Correct Answer
Option B
Solution
Given 2x+3y−z=5x+αy+3z=−43x−y+βz=7Δ2=213−13β5−47Δ2=2(21+4β)+1(7+12)+5(β−9)Δ2=42+8β+19+5β−45Δ2=13β+16Δ2=0∴β=−1316Δ3=2133α−15−47Δ3=2(7α−4)−3(7+12)+5(−1−3α)Δ3=14α−8−57−5−15αΔ3=−α−70Δ3=0α=−7013αβ=(13)(−70)(−1316)=+1120
Q164
Consider the matrix f(x)=cosxsinx0−sinxcosx0001. Given below are two statements : Statement I : f(−x) is the inverse of the matrix f(x). Statement II : f(x)f(y)=f(x+y). In the light of the above statements, choose the correct answer from the options given below :