Name: Ryan Grade 12 student

If sinA = 4/5, and A is a first quadrant angle, find sin4A

Hi Ryan

From the right triangle in the diagram with sin A = 4/5, Pythagoras' Theorem shows that the third side of the triangle has length 3 and hence cos A = 3/5. Use the exprression sin 2A = 2 sin A cos A to calculate sin 2A. Now start again. Since you know sin 2A use Pythagoras' Theorem to find cos 2A and hence calculate sin 4A. Cheers Harley