Rumus umum perkalian sinus-cosinus

$\sin\alpha\cos\beta=\frac{1}{2}\left(\sin\left(\alpha+\beta\right)+\sin\left(\alpha-\beta\right)\right)$

Dengan demikian

Hitung terlebih dahulu perkalian sinus-cosinus

$\sin90\degree\cos30\degree=\frac{1}{2}\left(\sin\left(90\degree+30\degree\right)+\sin\left(90\degree-30\degree\right)\right)$

$=\frac{1}{2}\left(\sin120\degree+\sin60\degree\right)$

$=\frac{1}{2}\left(\frac{1}{2}\sqrt{3}+\frac{1}{2}\sqrt{3}\right)$

$=\frac{1}{2}\sqrt{3}$

Selanjutnya hasil perkalian sinus-cosinus dikalikan dengan $\sin45\degree$

$=\frac{1}{2}\sqrt{3}\ .\ \sin45\degree$

$=\frac{1}{2}\sqrt{3}\ .\ \frac{1}{2}\sqrt{2}$

$=\frac{1}{4}\sqrt{6}$