1A(-1,0)B(3,0)C(0,3)x1=-1,x2=3x=0,y=c=3x1x2=c/a=-3a=-1x1+x2=2=-b/ab=2y= -x^2+2x+3对称轴x=-b/2a=(x1+x2)/2=1c-b^2/4a=3-4/(-4)=4 顶点P(1,4)直线BC：y-3=[(3-0)/(0-3)]x
y=-x+3
x=1,y=2M(1,2) P(1,4)2过P平行BC直线y-4=-(x-1)
y=5-x y=-x^2+2x+35-x=-x^2+2x+3x^2-3x+2=0(x-2)(x-1)=... |
