已知代数式14x+5-21x²的值是-2,求6x²-4x+5的值

问题描述:

已知代数式14x+5-21x²的值是-2,求6x²-4x+5的值

7
14x+5-21x²=-2,求的x=1或-1/3,代入6x²-4x+5=7亲x怎么求粗来的14x+5-21x²=-2可得21x^2+14x+7=0,即3x^2-2x-1=0,因式分解(3x+1)(x-1)=0.所以x=1或-1/3,代入6x²-4x+5=7