数学题化简2(x-3)(x+3)-(x+3)(3-x)其中x=12(x-3)(x+3)-(x+3)(3-x) 其中x=1

问题描述:

数学题化简2(x-3)(x+3)-(x+3)(3-x)其中x=1
2(x-3)(x+3)-(x+3)(3-x) 其中x=1

=2*(-2)*4-4*2=-24

中间减号为分界两部分来看左右边都可用平方差公式

2(x-3)(x+3)-(x+3)(3-x)
=2(x^2-3^3)+(x^2-3^3)
=3(x^2-3^3)
=3-27
=-24


(x-3)(x+3)(2+1)=3(x^2-9),因为x=1
所以原式=3*(-8)=-24

x=1
∴2(x-3)(x+3)-(x+3)(3-x)
=2(x²-9)+(x+3)(x-3)
=2x²-18+x²-9
=3x²-27
=3×1²-27
=3-27
=-24