Prove teh Identitiy

$\displaystyle

cosh (x+ y) = cosh x cosh y + sinh x sinh y

$

from the basic definitions of the hyperbolic functions. Hence, or otherwise show that if x and y satisfy the equations

cosh x cosh y = 2,

cosh x sinh y = -1

then x = -y = +or- ln (1+*squareroot* of 2)

I dunno how to use the math thingy too well so xD sorry if it's messed up.

This question just has me staring, don't even know what I should be doing.