About the maths question

H=(ad/b)-d^2

Hope I can help you.

a= b( c+d )

a= bc + bd

a-bd = bc

c = (a-bd) / b

then H = [ d(a-bd) ] / b

a=b(c+d)
a/b=c+d
(a/b)-d=c

H=cd
H=[(a/b)-d]*d
H=(ad/b)-d^2