Math Is Fun Forum

woweycowey

Member

Registered: 2012-10-20

Posts: 1

Please Help with this Trigonometry Proof!

If anyone could help with this that would be amazing, im just finding myself stuck.

(sinxcosx)/((cosx^2)-(sinx^2))  =  ((tanx)/(1-tanx^2))

Bob

Administrator

Registered: 2010-06-20

Posts: 10,803

Re: Please Help with this Trigonometry Proof!

hi woweycowey

Welcome to the forum!

I think you mean sin^2 (x) rather than sinx^2 ie.

Anyway start with the left hand side:

Divide top and bottom by

and it comes out straight away.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

zetafunc.

Guest

Re: Please Help with this Trigonometry Proof!

Bob bundy's way is the best way since it is only one step. Here is another neat way to do it but it takes a bit longer (it's how I did it though);

I still prefer the one-step method though, haha. So this post is a little redundant...

Bob

Administrator

Registered: 2010-06-20

Posts: 10,803

Re: Please Help with this Trigonometry Proof!

hi zetafunc,

That's what I thought as well to start with.  I think the double angle formulas jump out at you.

But I  thought the OP might not have met them so I looked to see if I could bypass them.  The tan2A formula comes from dividing by cos so I tried that instead and nearly fell off my chair.

Good to offer a choice so not redundant. 

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob