Tuesday, March 1, 2011

Proving Trigonometric Identities Prove: 1/ 1 + sinx = sec^2 x - tanxsecx

We need to prove
that:


1/(1+sinx) = sec^2 x -
tanx*secx


We will start from the right side an prove the
right side.


==> sec^2 (x) -
tanx*secx.


We know that sec(x) =
1/cos(x)


and tanx =
sinx/cosx


==> sec^2 x - tanx*secx =
(1/cosx)^2 -sinx/cosx *
1/cosx


                                          = 1/cos^2
x  - sinx/cos^2 x


                                        =
(1-sinx) / cos^2 x


But we know that: sin^2 x + cos^2 x =
1


==> cos^2 x = 1- sin^2
x


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


Now we will factor the
denominator.


==> (1-sinx)/cos^2 x=
(1-sinx)/(1-sinx)(1+sinx)


Now we will reduce
similar.


==> sec^2 x - tanx*secx = 1/(1+sinx) .....
q.e.d

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