Maclaurin's theorem help!!

Your answer is correct, they have forgotten to divide by 2.

As already said you are correct. Did you notice it is the expansion of coshx?

no we haven't learned about cosh and other trigs

cosh = hyperbolic cosine, so it isn't a trig function. If you know about the unit circle definition of trig functions, then basically to get the hyperbolic trig functions you do the same sort of thing but with a hyperbola instead of a circle. You should learn about them in FP2.