A Maths Trigonometry HELP!

• Nathpoop

  11 Jan 10, 17:28

  Can you help me with the following two questions?

  1. Prove the identity, (Sin A + Sin B)(Sin A - Sin B) = Sin(A + B)Sin(A - B)

  2. Prove that Sin X + Sin 2X + Sin 3X + Sin 4X = 4 Cos X/2 Cos X Sin 5X/2.

  Hence, find all the angles between 0 and pi for which

  Sin X + Sin 2X + Sin 3X + Sin 4X = 0 (Ans: pi/2, 2pi/5, 4pi/5)

  Thanks for helping me out! (:

• wee_ws

  11 Jan 10, 22:10

  Hi,

    For Q1, start from LHS. You will need to use suitable factor formulae and double-angle formula.

    For Q2, start from LHS and use a suitable factor formula three times. Use RHS expression to solve for X.

    Thanks!

  Cheers,
  Wen Shih