trig proof help please

Bookworm524

Help what happened from step 2 to 3? Why do minus signs disappear? I understand the other parts but just not that step

(edited 11 months ago)

Reply 1

davros

Original post by Bookworm524

Help what happened from step 2 to 3? Why do minus signs disappear? I understand the other parts but just not that step

sin is an odd function, so sin(-x) = -sin x. cos is an even function, so cos(-x) = cos x :smile:

Reply 2

Bookworm524

Original post by davros

sin is an odd function, so sin(-x) = -sin x. cos is an even function, so cos(-x) = cos x :smile:

um what does that mean? Thanks

Reply 3

user8937264980

Original post by Bookworm524

um what does that mean? Thanks

if you draw the graphs or use desmos and pick out a point for x you will be able to understand it better

Reply 4

davros

Original post by Bookworm524

um what does that mean? Thanks

it means what it says :biggrin:

A function is referred to as an "even function" if f(-x) = f(x) for all values of x in the domain. So in your case, we know that cos(-x) = cos x always, so that minus sign just "disappears". "sin x is an odd function" means that sin(-x) = -sin x for all values of x. In this case, that minus sign cancels the other minus sign you had on the numerator :smile: