1 more:
Solve the equation
sin5\theta =1 \text{for} 0<\theta<2\pi, \text{ and hence show that the roots of the equation }\\ 16x^2+16x^3-4x^2-4x+1=0 are x=sin\frac{(4r+1)\pi}{10} \text{,where r=0,2,3,4.}\\ \text{determine the exact value of } sin\frac{\pi}{10}sin\frac{3\pi}{10}