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View Full Version : Proving trig expression ((secx-tanx)^2 1)/(secxcscx-tanxcscx)=2tanx


hines57
Dec 12, 2011, 09:58 PM
((secx-tanx)^2 1)/(secxcscx-tanxcscx)=2tanx please help me with this if you can its got me stumped

Aurora2000
Dec 13, 2011, 03:28 AM
((\sec x-\tan x)^2+1)/(\sec x\csc x-\tan x \csc x) = 2\tan x

By direct computation:

Numerator:
(\sec x-\tan x)^2+1 =\sec^2 x+\tan^2 x-2\sec x\tan x+1 =
\frac{1}{\cos^2 x}+\frac{\sin^2x}{\cos^2x}-2\frac{1}{\cos x}\frac{\sin x}{\cos x}+1=
\frac{1+\sin^2 x}{\cos^2 x}- \frac{2\sin x}{\cos^2 x}+1= \frac{1+\sin ^2 x-2\sin x}{\cos^2 x}+1=
\frac{(1-\sin x)^2}{\cos^2 x} +1 = \frac{2(1-\sin x)}{\cos^2 x}

Denominator:

\sec x\csc x-\tan x \csc x = \frac{1}{\sin x\cos x}- \frac{\sin x}{\cos x}\frac{1}{\sin x}
=\frac{1}{\sin x\cos x} -\frac{1}{\cos x} =\frac{1-\sin x}{\sin x\cos x}

Then the original fraction reads

\frac{ \frac{2(1-\sin x)}{\cos^2 x} }{\frac{1-\sin x}{\sin x\cos x}}
= \frac{2(1-\sin x)}{\cos^2 x} \frac{\sin x\cos x}{1-\sin x}=
2\frac{\sin x}{\cos x}=2\tan x