Question

初二数学 先化简再求值

Answer 1

解：y(x+y)+(x-y)²-x²-2y²
=xy+y²+x²+-2xy+y²-x²-2y²
=-xy
又已知x=-1/3，y=3
∴-xy=-(-1/3×3)=-(-1)=1(负负得正)
∴y(x+y)+(x-y)²-x²-2y²=1

Answer 2

y(y+x)+(x-y)²-x²-2y²
=y²+xy+x²-2xy+y²-x²-2y²
=-xy
=-(-1/3)*3
=1

Answer 3

原式 =xy + y^2 + x^2 - 2xy + y^2 - x^2 - 2y^2
= -xy
因为x=- 1/3，y=3,
所以原式= - （- 1/3）*3=1

Answer 4

是y(x+y)+(x-y)2-x^2-2y^2吧
=yx+y^2-2x-2y-x^2-2y^2
=-x^2-y^2+xy-2x-2y
代入x=-1/3，y=3
=-1/9-9-1+2/3-6
=-15-4/9

Answer 5

原式=xy+y的平方+x的平方-2xy+y的平方-x的平方-2y的平方=-xy
将x=-1/3，y=3代入原式得1

Answer 6

题有问题，应该是（x-y)^2
原式=xy+y^2+x^2-2xy+y^2-x^2-2y^2=-xy
代入x=-1/3,y=3，原式=1.