Question

先化简,再求值6x²y+2xy-3x²y²-7x-5yx-4y²x²-

Answer 1

原式=-7x^2y^2-3xy-7x

∵Ix+3I+(y-1/2)^2=0,又Ix+3I≥0,（y-1/2)^2≥0,∴x+3=0,y-1/2=0,解之得：x=-3,y=1/2并代入上式得：-7*9/4+9/2+21=39/4