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This is a question that requires a bit of thinking out of the box. Because the triple angle identity is not taught in 'O' Level A-Math, you will need to instead "prove" the identity! Notice that 3x = 2x + x.

This question requires the use of the addition formula, double angle formulae, and trigonometric identities, so do recall and remember them.

For part (ii), use the answer in part (i) and express sin^3(x) in terms of sinx or sin3x. Substitute it into the expression and integrate accordingly.