(8)先化简再求值(2x-1)^2-(3x+1)(3x-1)-5x(x-1) 其中x=-1 (9)设a-b=-3,求2分之a^2+b^2-ab的值
问题描述:
(8)先化简再求值(2x-1)^2-(3x+1)(3x-1)-5x(x-1) 其中x=-1 (9)设a-b=-3,求2分之a^2+b^2-ab的值
答
(8)先化简再求值(2x-1)^2-(3x+1)(3x-1)-5x(x-1) 其中x=-1
(2x-1)^2-(3x+1)(3x-1)-5x(x-1)
=4x²-4x+1-9x²+1-5x²+5x
=-10x²+x+2
=-10-1+2
=-9
(9)设a-b=-3,求2分之a^2+b^2-ab
2分之a^2+b^2-ab
=1/2 (a²+b²-2ab)
=1/2 (a-b)²
=1/2 ×9
=9/2