# 3 quick question's on Identities

• May 3rd 2009, 01:09 PM
brentwoodbc
3 quick question's on Identities
1)How would you verify this numerically?
there is no given value of x so Im confused just use a calculator?
(pi/2+x)=sin(pi/2-x)

2)even when you get a given value of x I get confused like
cos(pi-x)=-cosx
when x=2.9

3)also if you are given a list of possible identities and are asked to say which ones are and which ones arent how do you do that? Just sketch it, I mean it worked for me but if you have a easier way Id love any input.
example

tan-x=tanx
tan-x=-tanx
sin(pi/2+x)=cosx
sin(pi/2-x)=cosx
thanks.
• May 3rd 2009, 01:29 PM
VonNemo19

Co-Function Identities

http://www.sosmath.com/trig/Trig5/trig5/img4.gif

Even-Odd Identities
http://www.sosmath.com/trig/Trig5/trig5/img5.gif

Visualizing what is happening on the graph with the unit circle situated with its center at the origin while an angle is rotating around and x and y constantly changing helps me to understand these identities.

I know it's confusing, but you'll get it.(Hi)