这道题怎么算(x-8)(-10x＋300)

题目

这道题怎么算(x-8)(-10x＋300)
(x-8)(-10x＋300) 是怎么算的 ＝-10(x-8)(x-30) ＝-10(x2-38x＋240) ＝-10(x-19)2＋1210

答案

（x-8)(-10x+300)=(x-8)[-10(x-30)]= -10(x-8)(x-30)=-10[x(x-30)-8(x-30)]=-10(x2-30x-8x+240)=-10(x2-38x+240)=-10[(x2-19*2x+19*19)-19*19+240]=-10[(x-19)2-361+240]=-10(x-19)2-1210