Question

3a^2-4ab+b^2-a^2+3ab-2b^2,其中a=0.9,b=-1

Answer 1

3a^2-4ab+b^2-a^2+3ab-2b^2

=2a^2-ab-b^2

当a=0.9,b=-1时,

原式=2*(0.9)^2-0.9*(-1)-(-1)^2

=2*0.81+0.9-1

=1.62+0.9-1

=1.52.