Originally Posted by

**furor celtica** Solve the following equation of A, giving solutions in the 0<A<360 inclusive (i don't know how to make the 'or equal to' sign):

sin2A - (sqrt3)(cos2A) =0

So I did it like this

Taking B=2A

sinB - (sqrt3)(sqrt(1-(sinB)^2)) = 0 (because cosB = sqrt(1-(sinB)^2)

sinB=sqrt(3-3(sinB)^2)

(sinB)^2=3-3(sinB)^2

4(sinB)^2=3

sinB=(plus or minus)sqrt3/2

from this I get the results A=30, 60, 120, 150, 210, 240, 300, 330

However, only 30, 120, 210 and 300 are correct.

Why is this?