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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