- #1

kalistella

- 4

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**addition formulae - Trig help requested!**

I have a problem with this with regard to Sin 120 or Cos 120.

Eg

sin 165

sin (120 +45)

sin120.cos45-cos120.sin45

How do I deal with sin 120 or cos 120?

I know that cos 45 is 1/square root 2 and so is sin 45.

But in the above problem, the answer comes to 1/4 (square root 6 - square root 2)

I don't get this answer. My problem is with the 120 angles.

Please help!

Thanks!