Can e^i(x+y) + e^-i(x+y) be Simplified to 2cosxcosy?

[ramses07]

Homework Statement

im wondering if e^i(x+y) + e^-i(x+y)

can be simplified to 2cosxcosy

Homework Equations

2cosx= e^ix + e^-ix



so i separated e^i(x+y) + e^-i(x+y)

into;

e^ix(e^iy) + e^-ix(e^-iy)

can that become 2cosxcosy?

 

[Dick]

It's 2*cos(x+y), isn't it? That's not the same thing as 2*cos(x)*cos(y).