I need help with a trigonometric reason

Question

Hi there, I was doint an integral and I need help with something about this

It seems that

(r² - r² • sin²(t)) = r² • cos² (t)

But I can't find why is this true anywhere, can you help me?

Thank you in advance!

Answer 1

You can factor r² out of the terms in the parentheses to get:

(r cos t) (r² - r²sin t) =(r cos t) (r²(1-sin²t)) = (r cos t)(r²cos²t) = r³cos³ t

Meaning you have typos on the right side.