# Thread: x = tanx

1. ## x = tanx

Can someone explain to me why xcosx - sinx = 0 when x = tanx?

Thanks.

2. ## Re: x = tanx

Replace tanx with sinx/cosx and it comes right out.

3. ## Re: x = tanx

Asked and answered in the other thread.

Please do not double post.

-Dan

4. ## Re: x = tanx

Let x = tan x. Then

x cos x - sin x
= tan x * cos x - sin x
= (sin x / cos x) * cos x - sin x
= sin x - sin x
= 0