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