Math problem (Simplifying an equation)

Question

The above equation simplifies to this:

I don't understand how though, please give a detailed step-by-step solution to the question.

Answer 1

combine like terms

a-b -(a-b) = a-a -b+b==0

the a's and b's all cancel

(1/2)L + (1/2)L = (1) L=L

leaving just 2 terms

L/sqr(1-v2/c^2) + L

factor out the L to get

L((1/sqr(1-v^2/c^2) +1)