???$解：(1)令y=0 ，得-x2+(m-2)x+ m+1 =0$???
???$因?yàn)閎2-4ac=(m-2)2+ 4(m+ 1)= m2+ 8> 0$???
???$所以一元二次方程有兩個(gè)不相等的實(shí)數(shù)根$???
???$所以這個(gè)二次函數(shù)的圖像必與x軸有兩個(gè)公共點(diǎn)$???
???$(2)令x=0，得y=m+1$???
???$所以這個(gè)二次函數(shù)與y軸的交點(diǎn)為(0 ， m+1)$???
???$由題意得，m+1<0$???
???$解得， m<-1$???
???$所以當(dāng)m<-1時(shí)，二次函數(shù)的圖像與y軸的交點(diǎn)在y軸的負(fù)半軸上$???
???$(3)由題意得，\frac {-(m-2)}{-2}=0$???
???$解得，m=2$???
???$所以當(dāng)m = 2時(shí)，這個(gè)二次函數(shù)的圖像的對(duì)稱軸是y軸$??
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