Posted by **May** on Monday, January 11, 2010 at 7:15pm.

Hi, could someone explain to me how to use a counterexample in trig to prove whether something is either an identity or equation?

For ex. how would you do that with this question?

sec^2x-tan^2x= cos x

- Math- gr.12 Trig. -
**Marth**, Monday, January 11, 2010 at 8:13pm
A counterexample is simply any instance that disproves the statement.

For example, try using x = pi/4. Note that this is NOT the only correct answer.

- Math- gr.12 Trig. -
**May**, Monday, January 11, 2010 at 8:19pm
Would I substitute the same number to both sides?

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