先化简再求值:3x2y-[2x2y-3(2xy-x2y)+5xy]，其中(x-2)2+|y+1|=0.

更新时间2022-06-13 07:08:24

∵ (x-2)²+|y+1|=0

∴ x=2，y=-1

3x²y-[2x²y-3(2xy-x²y)+5xy]

=3x²y-2x²y+3(2xy-x²y)-5xy

=x²y+6xy-3x²y-5xy

=xy-2x²y

=xy(1-2x)

=-1×2×(1-2×2)

=-2×(-3)

=6

已知x+y=7，xy=2，求下列各式的值。 (1)2x平方+2y平方的值 (2)(x-y)平方的值

x+y=7

(x+y)²=49

x²+y²+2xy=49

x²+y²=49-2×2=45

(1)

2x²+2y²

=2(x²+y²)

=2×45

=90

(2)

(x-y)²

=x²+y²-2xy

=45-2×2

=41