The question asks me to solve
So I put it into the form :
Then I equate the coefficients:
of cos x: 
of sinx: 
Divide  by  to get:
Square and add  and  to get:
Except that last statement doesn't seem to be true, according to
the answers in my book and when I have a look at the two curves in a
graphing application. I tried in the graphing app and
that seems to be correct...
What have I done wrong? Why am I getting a positive value for
alpha when I should be getting the same number but negative?
The only way I can see to get -49.4 would be by introducing a minus
sign when dividing  by . But I don't see how to justify that.
Have I made a simple error? I can't spot it ...
Any help would be much appreciated, thanks in advance.