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

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

人气：212 ℃　时间：2019-10-23 11:30:59

解答

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)