The first question asked to express a equivalent expression in of $\cos(x+y)$ for which I got right.
However its the second part of the question that I do not understand which is How to express $\sin(y)$ in terms of $\cos(y)$? also the angle between $0$ and $\frac { \pi }{ 2 } $
$\endgroup$2 Answers
$\begingroup$$$\sin { y } =\cos { \left( y-\frac { \pi }{ 2 } \right) } \\$$ or $$ \sin { y=\sqrt { 1-\cos ^{ 2 }{ y } } } $$
$\endgroup$ 0 $\begingroup$Recall the Pythagorean identity:
$$a^2+b^2=c^2$$
Divide both sides by $c^2$:
$$\sin^2(\theta)+\cos^2(\theta)=1$$
Solve for $\sin$.
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