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

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