Prove (algebraically) that: .
I'm not sure what "algebraically" means . . .
. . some Trigonometry must be used.
We have the identity: .
Add  and : .
"Prove (algebraically) that: "
I'm not sure if I should handle this like an identity or not... I'm well out of the identity chapter, so I don't know why I'd be asked this now.
I'm thinking the composite argument property might be of use?