Question

X＝－2分之1,y＝－3时,求代数式3（x的平方－2xy）－［3X的平方－2x的平方－2y＋2（xy+y）］的值

Answer 1

3(x²-2xy)-[3x²-2x²-2y+2(xy+y)]

=3x²-6xy-(x²+2xy+2y)

=2x²-8xy-2y

=2×﹙-½﹚²-8×﹙-½﹚×﹙-3)-2×﹙-3)

=½-12+6

=-5.5