# Multiplying Trigonometric Expressions

• Aug 3rd 2013, 03:46 PM
curt26
Multiplying Trigonometric Expressions
(cot(x)-tan(x))(cot^2(x)+1+tan^2(x))

The answer is cot^3(x) - tan^3(x)

I cannot get to the same outcome.

Any help would be great thanks!
• Aug 3rd 2013, 04:21 PM
HallsofIvy
Re: Multiplying Trigonometric Expressions
Well, then, what do you get? You see where "cot^3(x)" and "tan^3(x)" come from, don't you. So I guess your question would be "where did all the other terms go?" There are, in fact, four other terms: cot(x) times 1 and times tan^2(x) and -tan(x) times cot^2(x) and times 1. What do those give?

You know that "cot(x)tan(x)= 1", don't you?
• Aug 4th 2013, 12:03 AM
smatik
Re: Multiplying Trigonometric Expressions
have u done this identity in school(algebra): a^3-b^3=(a-b)(a^2+b^2+a*b)???Let a=cot (x) and b=tan(x) will give a*b=1.Still without identity if you merely solve R.H.S. you can get the desired L.H.S.
• Aug 4th 2013, 02:54 PM
curt26
Re: Multiplying Trigonometric Expressions
Thanks for the help! I think I got it