Thread: trigonometric identity proving need help

how should i start this

1 - cos^2 theta/ 1 + sin theta = (convert to) sin theta

please help

Originally Posted by xahjika

how should i start this

1 - cos^2 theta/ 1 + sin theta = (convert to) sin theta

please help

Recall that

it says that

prove that it is an identity

1 - cos^2 theta/ 1 + sin theta = sin theta

Originally Posted by xahjika

it says that

prove that it is an identity

1 - cos^2 theta/ 1 + sin theta = sin theta

I have figured it out, and made the edits. But please, in the future, be more clear and add parentheses.

That identity is not true. Are you sure you're written it correctly?

Edit: Ah right, I was reading it incorrectly also... nevermind.

so sorry i don't know that... i'm just copying what's on the board

Originally Posted by Chop Suey

Recall that

with that do i have to foil method this? --> (1 - sin theta)(1 + sin theta)/
1 + sin theta
or cancel the(1 + sin theta).. / 1 + sin theta here --> (1 - sin theta)(1 + sin theta)/ 1 + sin theta

is this right?

red means canceled out

1 - sin^2 theta =

(1 - sin theta) (1 + sin theta)/ (1 + sin theta)=

1 - ( 1 - sin theta) = sin theta

Originally Posted by xahjika

is this right?

red means canceled out

1 - sin^2 theta =

(1 - sin theta) (1 + sin theta)/ (1 + sin theta)=

1 - ( 1 - sin theta) = sin theta

Yes, you have to cancel out like you just did. There are inconsistencies in your work that you may have to fix.