Finding angles of intersection

Find x so that
sin(4x) == -cos(2x)

I perform:
sin(4x) == -sin(2x-a), a=pi/2
sin(4x) == sin(-2x+a)
4x == -2x + a +2pi*n
6x == a + 2pi*n
x == pi/12 + n*pi/3

Hence i get solutions:
pi/12 5pi/12 9pi/12

However, when plotted, it seems that i should get
four solutions (other than i got too). How should i
get to them?

--
Vänligen
Konrad
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Sleep - thing used by ineffective people
as a substitute for coffee

Ambition - a poor excuse for not having
enough sence to be lazy
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