# Multiply and simplify: frac{(sin theta+cos theta)(sin theta+cos theta)-1}{sin theta cos theta}

Question
Multiply and simplify: $$\frac{(\sin \theta+\cos \theta)(\sin \theta+\cos \theta)-1}{\sin \theta \cos \theta}$$

2021-02-22
Use the square of a binomal:
$$(a+b)^{2}=(a+b)(a+b)=a^{2}+2ab+b^{2}$$
$$=\frac{(\sin^{2}\theta+2\sin\cos \theta+\cos^{2}\theta)-1}{\sin \theta \cos \theta}$$
$$=\frac{(2\sin \theta \cos \theta+\sin^{2}\theta+\cos^{2}\theta)-1}{\sin \theta \cos \theta}$$
Use the Pythagorean identity: $$\sin^{2}\theta+\cos^{2}\theta=1$$
$$=\frac{(2\sin \theta\cos \theta+1)-1}{\sin \theta \cos \theta}$$
Simplify:
$$\frac{2\sin \theta \cos \theta}{\sin \theta \cos \theta}=2$$

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