# Thread: Prove the following identities

1. ## Prove the following identities

I'm not sure the working step.

tan x + tan y = sin(x + y) / cos x + tan y

This my ans;

LHS = sin x cos y + cos x sin y / cos x cos y
= sin x + sin y
= tan x + tan y
= RHS

2. ## Re: Prove the following identities

Hey choi105.

I think you may have copied this down wrong.

Do you mean sin(x+y)/[cos(x) + tan(y)] instead?

yup.

4. ## Re: Prove the following identities

The identity written is not true. Please recheck the question.

5. ## Re: Prove the following identities

sorry for typing error.
The que: tan x + tan y = sin(x + y) / cos x + cos y

6. ## Re: Prove the following identities

Again it is wrong. Check the Dinominator.

7. ## Re: Prove the following identities

I think RHS would be having cosx cos y in the denominator.
write tanx and tany in the form of sinx / cosx and siny/cosy. take LCM and use the formula for sum of angles the numerator and you have the result.