(1/4x^2y^3)^2+(3/4x^3y^4)×(-4xy) (a+b-c)(a+b+c)-[(a-b)^2+4ab]

题目

(1/4x^2y^3)^2+(3/4x^3y^4)×(-4xy) (a+b-c)(a+b+c)-[(a-b)^2+4ab]
已知2x=y,求代数式[（x^2+y^2)-（x-y)^2+2y(x-y）]+(4y)的值

答案

1)=(1/4x^2y^3)^2-3x^4y^5=1/16x^4y^5=x^4y^5(1/16y-3)
2)=(a+b)^2-c^2-(a-b)^2-4ab=a^2+2ab+b^2-c^2-a^2+2ab-b^2-4ab=-c^2
3)=(x^2+y^2-x^2+2xy-y^2+2xy-2y^2)+4y=4xy-2y^2+4y
因为y=2x
所以=2y^2-2y^2+4y=4y