Question

若x的绝对值=2,求下列式的值：3x^2-((7x^2-2(x^2-3y)-2x))

Answer 1

1.x=2时

3x^2-[7x^2-2(x^2-3y)-2x]

=3x^2-[7x^2-2x^2+6y-2x]

=3x^2-5x^2-6y+2x

=-2x^2-6y+2x

=-2*2^2-6y+2*2

=-4-6y

=-2(3y+2)

1.x=-2时

3x^2-[7x^2-2(x^2-3y)-2x]

=3x^2-[7x^2-2x^2+6y-2x]

=3x^2-5x^2-6y+2x

=-2x^2-6y+2x

=-2*(-2)^2-6y+2*(-2)

=-12-6y

=-6(y+2)