Monday, June 10, 2013

trignometric identities: prove 1/sinθ-sinθ≡cosθ/tanθ

We need to prove that
:


1/sin(x) - sinx/tanx = cosx/
tanx


We will start from the right side and prove the left
side.


==> cos x/
tanx


But we know that tan(x)= sinx /
cosx


We willl
substitute:


==> cosx / (sinx/cosx) = cosx* cosx/
sinx = cos^2 x / sinx


But we know that cos^2 x = 1- sin^2
x


==> (1- sin^2 x) / sinx = 1/sinx - sin^2 x/ sinx =
1/sinx - sinx


==> Then we prove that
cosx/ tanx = 1/sinx - sinx

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