# Homework Help: Precalculus: proving trigonometric identity

1. Mar 9, 2010

### jessicagu93

1. The problem statement, all variables and given/known data

prove that: tan(1+cos(x))^2 = 1-cos(x)

2. Relevant equations

trig identities, like the pythagorean, sum/difference, double/half angle identities, power reducing identities, etc...

3. The attempt at a solution

i'm not sure where to start; i tried using the pythagorean identity where 1+tan(X)^2 = sec(x)^2, but couldn't get anywhere after that :\

then i used my calculator and made X a random number. i typed in the left side expression, and pressed enter. i then typed in the right hand expression, and pressed enter. the two values were different. what did i do wrong?
i'm not really sure anymore that its even possible to prove the above...

2. Mar 9, 2010

### Dick

You're right. It's not an identity. Just put x=0. Then you don't even need a calculator. Must be some mistake here.

3. Mar 10, 2010

### snshusat161

If I'm write you want to write $$tan(1 + cos x)^2$$ = 1 - cos(x). I think it is not possible to prove because if cos (x) is zero then $${tan}^2{1}$$ is not equal to 1. Even if the equation is $$tan(1 + {cos}^2{x})$$ then also you can't prove it. I think, the problem is not to prove but to solve.