Answer:
u = [tex]\frac{b-a}{a+b}[/tex]
Step-by-step explanation:
Given
[tex]\frac{a}{1-u}[/tex] = [tex]\frac{b}{1+u}[/tex] ( cross- multiply )
a(1 + u) = b(1 - u) ← distribute parenthesis on both sides
a + au = b - bu ( add bu to both sides )
a + au + bu = b ( subtract a from both sides )
au + bu = b - a ← factor out u from each term on left side
u(a + b) = b - a ← divide both sides by (a + b)
u = [tex]\frac{b-a}{a+b}[/tex]
