AQA FP3 Maclaurin

I'm using the F3 book from the AQA website and am trying to do question Exercise 1B q 6.

I've looked at the Maclaurin's derivation on page 9 of the document but am non the nearer.

Could someone please give me a clue as to where to start.

Below is the particular question and a link to the book - book too large to upload.

http://filestore.aqa.org.uk/subjects/AQA-MFP3-TEXTBOOK.PDF

Start by assuming that $f(x+a)=a_1+a_2x+a_3x^2+\dots$
Putting x=0 immediately gives $a_1=f(a)$
Now just repeatedl;y differentiate and put x=0 to get the values of $a_i$

Ah, I thought I had to put (x-a) where the x's were.

Thanks

Could you also explain why I'm getting 1 instead of 2 for the first term of the expansion of 0.5(e^x + e^-x)
In fact all my terms are half the answer in the book. It's question 5 in exercise 1B.

I'm setting f(0) = 0.5(e^0 + e^(-0)) = 0.5(1+1) = 0.5(2) = 1.

Then odd terms turn to zero and even terms turn to 1.

Ah, I thought I had to put (x-a) where the x's were.

Thanks

Could you also explain why I'm getting 1 instead of 2 for the first term of the expansion of 0.5(e^x + e^-x)
In fact all my terms are half the answer in the book. It's question 5 in exercise 1B.

I'm setting f(0) = 0.5(e^0 + e^(-0)) = 0.5(1+1) = 0.5(2) = 1.

Then odd terms turn to zero and even terms turn to 1.

The answer in the book is wrong. they have given the answer for $e^x+e^{-x}$