# Thread: AP Calculus Verifying a Solution to a Differential Equation Trig Function (question)

1. ## AP Calculus Verifying a Solution to a Differential Equation Trig Function (question)

why did the -sin^2(x) change into -1 + cos^2x?

2. ## Re: AP Calculus Verifying a Solution to a Differential Equation Trig Function (questi

$\displaystyle \sin^{2}x+\cos^{2}x = 1.$

3. ## Re: AP Calculus Verifying a Solution to a Differential Equation Trig Function (questi

i don't get it

4. ## Re: AP Calculus Verifying a Solution to a Differential Equation Trig Function (questi

Originally Posted by asilvester635
i don't get it

Do you get that if $\displaystyle s^2+c^2=1$ then $\displaystyle -s^2=-1+c^2~?$

5. ## Re: AP Calculus Verifying a Solution to a Differential Equation Trig Function (questi

It's a basic trig identity that by now, (judging by what you are doing), you should be familiar with.

It can be rewritten as

$\displaystyle -\sin^{2}x = -1 +\cos^{2}x.$

6. ## Re: AP Calculus Verifying a Solution to a Differential Equation Trig Function (questi

yah i forgot its a trig identity.. thanks anyways