# Triple angle proof

#### Skelly4444

##### New member
How can (cos3x / sinx) + (sin3x / cosx) be identically equivalent to 2cot2x

I have tried rewriting everything but cannot seem to get anywhere with this?

Any advice would be greatly appreciated.

#### lev888

##### Elite Member
What have you tried?

#### Dr.Peterson

##### Elite Member
How can (cos3x / sinx) + (sin3x / cosx) be identically equivalent to 2cot2x

I have tried rewriting everything but cannot seem to get anywhere with this?

Any advice would be greatly appreciated.
I would first combine it into one fraction. Then I'd recognize something familiar. Something different might work better for you, but we'll know that after we've seen your work.

#### Skelly4444

##### New member
Thanks for responding, I've actually managed to work it out by using common denominator of sinxcosx and then recognising that the top of the fraction is the addition format for cos(3x - x) which obviously equates to cos2x. From here, it was quite straight forward.

#### Subhotosh Khan

##### Super Moderator
Staff member
Thanks for responding, I've actually managed to work it out by using common denominator of sinxcosx and then recognising that the top of the fraction is the addition format for cos(3x - x) which obviously equates to cos2x. From here, it was quite straight forward.
Nice work !!