The series

is a least squares Chebyshev polynomial approximation of f(x) on [-1,1], if

Find the quadratic least squares Chebyshev polynomial approximation of

, on .

-----------------------------

Their answer (I don't know where I went wrong):

---------------

My working:

Let (to map to [-1,1] interval).

.

.

Then

So, (you can compute on Maple),

So

Then to map back to ,

.

Now, simplifying is optional, but this answer is not correct (apparently).

Any idea what I did wrong? Or is this the wrong forum for this stuff?