2(x^2+y^2) / х^2-xy+y^2= 2(x^2+y^2) / (x-y)^2 =
= 2(x+y)(x-y) / (x-y)^2= 2(x+y) / (x-y) = - 2(x-y) / x-y= -2
А - 10b = 0
a = 10b
b = a/10
20 = 10*2 a=20, b=2
30 = 10*3 a=30, b=3
40 = 10*4 a=40, b=4
3b-2a = 0
3b = 2a
b = 2a/3
a = 3b/2
3*4 = 2*6 a=6, b=4
3*6 = 2*9 a=9, b=6