Part (a) should be relatively simple. Express the lengths of breadths of the rectangle in terms of sin and cos.

Part (b) requires the use of R formula in which R is always positive and alpha is always acute. By using the compound formula for cos (A - B) which is found in the mathematics formula sheet provided, i can derive the 2 equations and solve for R and alpha.

Part (c) should also be relatively simple. Just use double angle formula for sin and you will get your answer.