The following fraction is the simplest A 2x/x^2+1 B4/2x Cx-1/x^2-1 D1-x/x-1

The following fraction is the simplest A 2x/x^2+1 B4/2x Cx-1/x^2-1 D1-x/x-1

D is the simplest fraction
A can be changed to (2 * x divided by X * x) + 1 = (2 divided by x) + 1
B can be 2 * 2 divided by 2 * x = 2 divided by X
C can be (x-1) divided by (x-1) (x + 1) = 1 / (x + 1)