# Math Help - finding trignometric derivatives

1. ## finding trignometric derivatives

find dy/dx
y=1+x-cos(x)
-------------------------
ok so I got confused with the Pythagorean trig identities and 1 - cos(x) does NOT equal sin(x)
I guess I need help STARTING the problem

2. if $
f(x) = 1 + x - \cos x
$
you only must aplied the sum rule, I mean

$
f'(x) = \left( 1 \right)^\prime + \left( x \right)^\prime - \left( {\cos x} \right)^\prime = 0 + 1 - \left( { - \sin x} \right)
$

If you don`t know how find the derivate of sin(x), is aplied the definition

$
\mathop {\lim }\limits_{h \to 0} \frac{{\cos \left( {x + h} \right) - \cos \left( x \right)}}
{h}
$