find d in the equation 8=d^1/2
$$8=d^{\frac{1}{2}}$$
Raise both sides to the 2nd power:
$$8^2 = (d{^\frac{1}{2}})^2$$
$$8^2 = d^{\frac{1}{2}\times2}$$
$$8^2 = d^{\frac{2}{2}}$$
$$8^2 = d$$
$$64 = d$$
So:
$$\mathbf{d = 64}$$