Question

已知m=3x^2-2xy+y^2,n=2x^2+xy-3y^2,当x=-3,y=1/3时,求代数式3m-2n的值

Answer 1

3M-2N

=3(3X^2-2XY+Y^2)-2(2X^2+XY-3Y^2)

=9x^2-6xy+3y^2-4x^2-2xy+6y^2

=5x^2-8xy+9y^2

=5*9-8*(-3)*(1/3)+9*(1/9)

=45+8+1

=54