√n √n- √m √m
( ------------ - ---------------------) : ------------ =
√m+√n √n √n
√n² - (√n-√m)(√m+√n ) √n √n²-√n²+√m²
= ------------------------------------ *---------- = -------------------------- =
(√m+√n ) * √n √m (√m+√n ) *√m
√m
= --------------
(√m+√n )