# How to convert sin to cos?

There are a number of formulas that you can use to convert sin(a) to cos(a):

1. $\mathrm{sin}\left(a\right)=\mathrm{cos}\left(90-a\right)$
2. $cos\left(\alpha \right)=±\sqrt{1-si{n}^{2}\left(\alpha \right)}$
3. ${e}^{±ia}=\mathrm{cos}\left(a\right)±i\mathrm{sin}\left(a\right)$