# Strategies for Proving Identities by 73jiEX9y

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```									                          Strategies for Proving Identities

1.   Learn the basic identities so they come to mind readily.

2.   Pick the side you wish to work with. Usually it is easier to start with the more
complicated side.

3.   Look for algebraic things to do:
a.    If there are two terms, you want only 1
ii.    factor something out
b.    Multiply by a clever form of 1
i.     to multiply a numerator or denominator by its conjugate or
ii.    to get a desired expression in the numerator or denominator.
c.    Do any obvious algebra such as distribute like terms, squaring, or multiplying
polynomials.

4.   Look for trigonometric things to do.

a.    Look for familiar trig expressions like:

sin 
1  cos2           cos sec
cos

b.    If there are squares of functions, think of Pythagorean properties.

c.    Reduce the number of different functions, transforming them to the ones you

5.   Keep looking at the answer to make sure you are headed in the right direction.

6.   When you don’t know what to do, just try something!!

You are allowed to simplify both sides of the = sign, however nothing can be
moved across the = sign and nothing can be added, subtracted, multiplied,
or divided to the entire identity.
Examples:

1.   csc  sin  1

2.   cot 2   sec2  tan2   csc2 

cos  sin 
3.                sec2   tan 2 
sec  csc 

4.   (tan2 x 1)(cos2 x 1)   tan2 x

5.   tan x  cot x  sec x csc x

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