已知x²-x-1的值是0求x³-x²-x+5和(3x²+5x+2)-(x²+7x)的值
问题描述:
已知x²-x-1的值是0求x³-x²-x+5和(3x²+5x+2)-(x²+7x)的值
答
x³-x²-x+5
=x(x²-x-1)+5
=x*0+5
=5
(3x²+5x+2)-(x²+7x)
=3x²+5x+2-x²-7x
=2x²-2x+2
=2x²-2x-2+4
=2(x²-x--1)+4
=2*0+4
=4