The eccentricity of the curve $ 2x^2 + y^2 - 8x - 2y + 1 = 0 $ is:
Let $ f(x) = \int \frac{x^2 \, dx}{(1 + x^2)(1 + \sqrt{1 + x^2})} $ and $ f(0) = 0 $, then the value of $ f(A) $ is: