$證明：(1)將點(diǎn)(r，0)代入y_1，得$
$r^2+br+a=0$
$∵r≠0$
$∴等式兩邊同時(shí)除r^2得 $
$\frac {a}{r^2}+\frac {r}+1=0$
$即a(\frac {1}{r})^2+b×\frac {1}{r}+1=0$
$∴\frac {1}{r}是ax^2+bx+1=0的解$
$∴函數(shù)y_2的圖像經(jīng)過點(diǎn)(\frac {1}{r}，0)$
$(2)由題意可知y_2圖像開口向上，a＞0$
$m=\frac {4×1×a-b^2}{4×1}=a-\frac {b^2}{4}$
