若x^2-4x-1=0,则3x^2+12x-5的值现已更正：若x^2+4x-1=0,则3x^2+12x-5的值_数学解答

若x^2-4x-1=0,则3x^2+12x-5的值
现已更正：若x^2+4x-1=0,则3x^2+12x-5的值

人气：289 ℃　时间：2020-06-21 05:19:22

解答

因x^2+4x-1=0
则 x^2+4x = 1
那么
3x^2+12x-5 = 3(x^2+4x) -15 = 3*1-15 = -12