Here’s a  sample SPM Question that requires you to use Double Angle and Half Angle Formulae.

Given that sin x = 5/13, and that  x is obtuse. Calculate without using a calculator the value of

a) tan 2x

b) cos (x/2)

The technique used here is the same as for the Addition Formulae which I explained in this video.


a) -120/119

b) Square root of (1/26)

Here’s the Video Tutorial if you’re stuck.

Part 1 (Question a)

Part 2 (Question b)

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