Question

Why is sin 10= cos 80

Answer 1

Hint:   $\bf \textit{Cofunction Identities} \\ \quad \\ sin\left(90^o-{{ \theta}}\right)=cos({{ \theta}})\qquad \boxed{cos\left(90^o-{{ \theta}}\right)=sin({{ \theta}})} \\ \quad \\ \quad \\ tan\left(90^o-{{ \theta}}\right)=cot({{ \theta}})\qquad cot\left(90^o-{{ \theta}}\right)=tan({{ \theta}}) \\ \quad \\ \quad \\ sec\left(90^o-{{ \theta}}\right)=csc({{ \theta}})\qquad csc\left(90^o-{{ \theta}}\right)=sec({{ \theta}})$