$$\frac{b^{4}}{d^{4}}-21\frac{b^{2}}{d^{2}}+100$$
$-\frac{21\left(bd\right)^{2}}{d^{4}}+\left(\frac{b}{d}\right)^{4}+100$
$\frac{42b^{2}}{d^{3}}-\frac{4b^{4}}{d^{5}}$
