# Why are reference angles necessary in trig

Why are reference angles necessary in trigonometry. I understand they are the acute version of an obtuse angle.

tiny-tim
Homework Helper
Hi Luke77!
Why are reference angles necessary in trigonometry.

I've never come across them before.

Apparently, they're the difference between the angle and the nearest multiple of 180° (π).

(so they're always between 0° and 90°)

In other words, trig tables only give you measurements up to 90°, so you find the "reference angle", look up the trig of that in the trig table, and if necessary multiply by minus-one.

(see http://www.mathwarehouse.com/trigonometry/reference-angle/finding-reference-angle.php for some examples)

HallsofIvy