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Questions  

cos2x+asinx=2a7possesses  a  solution  for:

a
all a
b
a>6
c
a<2
d
a∈2,6

detailed solution

Correct option is D

We have cos2x+asinx=2a−7⇒1−2sin2x+asinx=2a−7⇒2sin2x−asinx+2a−8=0⇒sinx=a±a2−16a−44                      = a±a−84⇒ sinx=a−42 (or) 2Since sinx≠2, we have sinx=a−42Now      −1≤sinx≤1 ⇒   −1≤a−42 ≤1⇒        2≤a≤6

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