1) a2 - b2 / 6a2b2 : a+b/3ab

2) a2b-4b3/3ab2 * a2b/a2-2ab

3) x2-xy/x2+xy * x2y + xy2/xy

1) a2-b2/6a2b2 : a+b/3ab = (a-b) (a+b) / 3ab*2ab * 3ab/a+b = a-b/2ab

2) a2b-4b3/3ab2*a2b/a2-2ab = b (a2-4b) / 3ab2 * a2b/a (a-2b) = (a-2b) (a+2b) / 3a (a-2b) =

a+2b/3a

3) x2-xy/x2+xy * x2y + xy2/xy = x (x-y) / x (x+y) * y = y (x-y) / x+y