# trig

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Find all solutions in the interval [0,2pi].

sin 2x + sin x = 0

• trig -

sin 2 x = 2 sin x cos x

2 sin x cos x + sin x = 0

sin x (2 cos x + 1) = 0
so
x = 0 is a solution and x = 180 is a solution
then
cos x = -1/2
that is at x = 120 and x = 240

• trig -

We should also include 360° , (from sinx = 0)

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