Question 12 Marks
If $\sin \theta=\frac{11}{61}$ find the values of cosθ using trigonometric identity.
Answer
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$\sin ^2 \theta+\cos ^2 \theta=1$
$\Rightarrow\left(\frac{11}{61}\right)^2+\cos ^2 \theta=1$
$\Rightarrow \frac{121}{3721}+\cos ^2 \theta=1$
$\Rightarrow \cos ^2 \theta=1-\frac{121}{3721}=\frac{3600}{3721}$
$\Rightarrow \cos \theta=\frac{60}{61}$
$\sin ^2 \theta+\cos ^2 \theta=1$
$\Rightarrow\left(\frac{11}{61}\right)^2+\cos ^2 \theta=1$
$\Rightarrow \frac{121}{3721}+\cos ^2 \theta=1$
$\Rightarrow \cos ^2 \theta=1-\frac{121}{3721}=\frac{3600}{3721}$
$\Rightarrow \cos \theta=\frac{60}{61}$

