Question

$\mathrm{If}\cos B=\frac{3}{5}\mathrm{and}\left(A+B\right)=90°,\mathrm{then}\mathrm{find}\mathrm{the}\mathrm{value}\mathrm{of}\sin A.$

Answer 1

$$\begin{gathered} \mathrm{We}\mathrm{have}, \\ \cos B=\frac{3}{5} \\ \Rightarrow \cos \left(90°-A\right)=\frac{3}{5}\left(\mathrm{As},A+B=90°\right) \\ \therefore \sin A=\frac{3}{5} \end{gathered}$$