## anonymous one year ago Verify the Identity cos(x+pi/2)=-sinx

1. zepdrix

Hey :) Cosine Angle Sum Identity will be useful here!

2. zepdrix

$\large\rm \cos\left(\color{royalblue}{A}+\color{orangered}{B}\right)=\cos \color{royalblue}{A} \cos \color{orangered}{B}-\sin \color{royalblue}{A} \sin \color{orangered}{B}$

3. zepdrix

$\large\rm \cos\left(\color{royalblue}{x}+\color{orangered}{\frac{\pi}{2}}\right)=?$Plug the values into the formula, and simplify! :)

4. anonymous

cos(x)cos(pi/2)-sin(x)sin(pi/2)?

5. zepdrix

Mmm good! :) Now simplify cos(pi/2) and the sin(pi/2)

6. anonymous

-sin(x)

7. anonymous

@zepdrix ?

8. zepdrix

You're trying to get to -sin(x), yes. But you're missing a step.$\large\rm \cos\left(x+\frac{\pi}{2}\right)=\cos x \color{orangered}{\cos\frac{\pi}{2}}-\sin x \color{orangered}{\sin\frac{\pi}{2}}$You have to come up with values for these orange parts.