# Prove tan(y)

#### pl0oper

##### New member

I'm stuck. I need help. I need to see the whole process to know how to solve it.

Thank You!

#### Subhotosh Khan

##### Super Moderator
Staff member
View attachment 21588
I'm stuck. I need help. I need to see the whole process to know how to solve it.

Thank You!
Start with expanding cos(x+y), cos(x-y), sin(x+y) & sin(x-y) and simplifying the right-hand-side of the given identity.

Please show us what you have tried and exactly where you are stuck.​
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#### pka

##### Elite Member
$$\sin (x \pm y) = \sin (x)\cos (y) \pm \sin (y)\cos (x)$$
$$\cos (x \pm y) = \cos (x)\cos (y) \mp \sin (x)\sin (y)$$

SEE HERE I_______________SEE HERE II