若x²-3x+1=0,求2005-8x+x³的值

2024-12-28 09:01:59
推荐回答(2个)
回答1:

因为x²-3x+1=0,所以x²-3x=-1,2005-8x+x³ = x³ - 3x² + 3x² - 8x + 2005 = x(x²-3x) + 3x² - 8x + 2005 = -x + 3x² - 8x + 2005 = 3x² - 9x + 2005 = 3(x²-3x) + 2005 = -3 + 2005 = 2002

回答2:

所求=x^3-8x+2005=x^3-3x^2+x)+3x^2-9x+3+2002=x(x^2-3x+1)+3(x^2-3+1)+2002=x*0+3*0+2002=2002