I know questions similar to this have been answered previously so do not simply

Question

I know questions similar to this have been answered previously so do not simply link me to those problems. When I try to follow those directions I get the wrong answer. I might just be simplifying wrong. Please include all work. Thanks.

A nonconducting disk of radius a lies in the z = 0 plane with its center at the origin. The disk is uniformly charged and has a total charge Q. Find Ez on the z axis at the following positions. (Assume that these distances are exact. Use the following as necessary: Q, a, and epsilon0.)

Explanation / Answer

E = 2 pi k sigma (1 - z/(z^2+a^2)^0.5)

==> E = 2 pi (1/(4 pi e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

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a)

z = 0.3a

E = (1/(2 e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (0.3a)/((0.3a)^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (0.3)/((0.3)y2+1)y0.5)

==> E = (0.113) (Q/(a^2 e0))

b)
z = 0.5a

E = (1/(2 e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (0.5a)/((0.5a)^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (0.5)/((0.5)y2+1)y0.5)

==> E = (0.0880) (Q/(a^2 e0))

c)

z = 0.7a

E = (1/(2 e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (0.7a)/((0.7a)^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (0.7)/((0.7)y2+1)y0.5)

==> E = (0.0679) (Q/(a^2 e0))

d)

z = a

E = (1/(2 e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (a)/((a)^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (1)/((1)y2+1)y0.5)

==> E = (0.0466) (Q/(a^2 e0))

e)

z = 2a

E = (1/(2 e0)) (Q/(pi a^2)) (1 - z/(z^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (2a)/((2a)^2+a^2)^0.5)

==> E = (1/(2 e0)) (Q/(pi a^2)) (1 - (2)/((2)y2+1)y0.5)

==> E = (0.0168) (Q/(a^2 e0))

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