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# C3/C4 Trig watch

1. Hi
(i asked this question a couple of weeks ago but the replys wont come up so im asking again)

A 2 mark question in a c3 paper:
solve
arcsinX=arccosX

i have made the subtitution arccosx=y so x=cosy but im kind of stuck after this

(it is INCORRECT to assume sinx=cosx)

Thanks
2. OK so
arcsinx=arccosx
arccosx=y
cosy=x
arcsinx=y
siny=x
now REMEMBER cos(Θ)=sin(π/2-Θ)
so cosy=sin(π/2-y)
x=sin(π/2-y)
arcsinx=π/2-y (arcsinx=y)
y=π/2-y
2y=π/2
y=π/4
sinπ/4=x=1/root2
substitute this answer into each side of the equation and you should get the same answer

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Updated: June 14, 2016
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