Answer
Ans. a. 4√5/9, b. -1/9
Work Step by Step
Given:- cosθ=2/3
a. Sin2θ=2cosθsinθ
=$2\sqrt {1-cos^2θ}$cosθ
=2$\sqrt {1-4/9}$×2/3
=4√5/9
Ans.
b. $Cos2θ=cos^2θ-sin^2θ$
=$cos^2θ-1+cos^2θ$
=$2cos^2θ-1$
=2×4/9-1
=-1/9
Ans.
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