Вычислите x^2-5xy+2y^2/4x^2+xy-9y^2, если x: y=5: 2

X/y=5/2->x=5/2y
x^2-5xy+2y^2/4x^2+xy-9y^2=(5/2y)^2-5*(5/2y)*y+2y^2/(4*(5/2y)^2)+y*(5/2y)-9y^2=25/4y^2+2/(100/4)+5/2y^2-9y^2=y^2*(25/4-25/2+5/2-9)+2/25=y^2*(-51/4)+2/25