Simplify the following equation [K-L2-K+L2]4K = a/b

$\frac{\left[\right(K-L)2-K+L2]}{4K} = \frac{a}{b}\frac{K2+L2-2KL-K2+L2+2KL}{4K}= \frac{a}{b}$

=> - 4KL/4K = a/b

=> L = - a/b

=> bL = -a