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Question: Answered & Verified by Expert
Let dR, and A=-24+dsinθ-21sinθ+2d52sinθ-d-sinθ+2+2d, θ0, 2π. If the minimum value of detA is 8, then a value of d is:
MathematicsDeterminantsJEE MainJEE Main 2019 (10 Jan Shift 1)
Options:
  • A 22+2
  • B 22+1
  • C -5
  • D -7
Solution:
2370 Upvotes Verified Answer
The correct answer is: -5

A=-24+dsinθ-21sinθ+2d52sinθ-d-sinθ+2+2d

R3R3-2R2+R1

=-24+dsinθ-21sinθ+2d100

=14+dd-sinθ+2sinθ-2

=4d+d2-sin2θ+4=d+22-sin2θ

We know that 0sin2θ1

Given, the minimum value of A=8, which is possible, when sin2θ=1

d+22=9

d+2=±3

d=1 or d=-5.

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