>>28
y = x/3
x = 10の時、y=10/3

(x+3y)^2 -(x+2y)(x-2y) = x^2 +6xy +9y^2 -(x^2 -4y^2) = 6xy+13y^2

判読不能

x^2 -13x+36 = (x-4)(x-9)