Answer:
∫ x/√(1 - 4·x^2) dx
Subst. z = 1 - 4·x^2
1 dz = -8·x dx
dx = -1/(8·x) dz
∫ x/√(z)·(-1)/(8·x) dz
∫ -0.125/√(z) dz
∫ -0.125·z^(-0.5) dz
-0.25·z^(0.5) + C
-0.25·√(z) + C
Resubst.
-0.25·√(1 - 4·x^2) + C
