Question

已知mxy满足(1)(x－5)²＋|m－1|＝0；(2)-2ab的y＋1的次方与4ab³是同类项。求代数式

(2x²－3xy＋6y²)－m(3x²－xy＋9y²)的值

Answer 1

平方项与绝对值项均恒非负，两非负项之和=0，两非负项分别=0
x-5=0 x=5
m-1=0 m=1
同类项各参数的指数对应相等，y+1=3 y=2
(2x²-3xy+6y²)-m(3x²-xy+9y²)
=(2-3m)x²-(3-m)xy+3(2-3m)y²
=(2-3m)(x²+3y²)-(3-m)xy
=(2-3×1)(5²+3×2²)-(3-1)×5×2
=-37-20
=-57

Answer 2

x=5,m=1.y=1.