Exercise 5.4.3 solution
\(\sin A=\frac{4}{5}\quad\cos A=\frac{3}{5}\)
\(\sin3A=\sin(A+2A)=\sin A\cos2A+\cos A\sin2A=\sin A(\cos^2A-\sin^2A)+\cos A(2\sin A\cos A)=\frac{44}{125}\)
\(\sin A=\frac{4}{5}\quad\cos A=\frac{3}{5}\)
\(\sin3A=\sin(A+2A)=\sin A\cos2A+\cos A\sin2A=\sin A(\cos^2A-\sin^2A)+\cos A(2\sin A\cos A)=\frac{44}{125}\)