Question

若丨2x-5丨+(2x-5y+20)^2=0,求代数式(-2x^2)-2x(5y-2x)=3y(6x-5y)-3y(4x

Answer 1

若丨2x-5丨+(2x-5y+20)^2=0

∴2x-5=0;

x=5/2;

2x-5y+20=0;

y=5;

(-2x^2)-2x(5y-2x)-3y(6x-5y)-3y(4x-5y)

=-2x²-10xy+4x²-18xy+15y²-12xy+15y²

=2x²+30y²-40xy

=2*(25/4)+30*25-40*(5/2)*5

=25/2+750-500

=250+25/2

=262.5