ax-b=c, for x
a=h(a+b)/2, for h
ax-b = c, for x
Add b to both sides
x = b + c
Divide both sides by a
x = ( b + c) / a
Multiply both sides by 2
2a = h (a + b)
Divide both sides by (a + b)
2a / ( a + b) = h