再问一道jj数学

qinyitian

MingLiU","serif"; mso-font-kerning: 0pt; mso-bidi-font-family: PMingLiU;">1.        有条直线方程是MingLiU","serif"; mso-font-kerning: 0pt; mso-fareast-font-family: 宋体; mso-bidi-font-family: Tahoma; mso-fareast-language: ZH-CN;">ax+3y+1=0，MingLiU","serif"; mso-font-kerning: 0pt; mso-fareast-font-family: 宋体; mso-bidi-font-family: Tahoma; mso-fareast-language: ZH-CN;">a是一个正的常数，问下列哪一个可能是这条线在MingLiU","serif"; mso-font-kerning: 0pt; mso-fareast-font-family: 宋体; mso-bidi-font-family: Tahoma; mso-fareast-language: ZH-CN;">x轴上的截距MingLiU","serif"; mso-font-kerning: 0pt; mso-bidi-font-family: Tahoma;">
            

答案MingLiU","serif"; mso-font-kerning: 0pt; mso-fareast-font-family: 宋体; mso-bidi-font-family: Tahoma; mso-fareast-language: ZH-CN;"> -2MingLiU","serif"; mso-font-kerning: 0pt; mso-bidi-font-family: Tahoma;">
        

MingLiU","serif"; mso-font-kerning: 0pt; mso-bidi-font-family: Tahoma;">

MingLiU","serif"; mso-font-kerning: 0pt; mso-bidi-font-family: Tahoma;">请问这道题是不是叙述有问题啊，如果截距是-2，那a 不就等于-1/2了么？