(1)m是方程x^2+3x-4=0的解,
∴m=1或-4.
设B(b,0),b>0,则
AB^2=m^2+b^2=20,
b^2=19,或4,
∴A(0,1),B(√19,0)或A(0,-4),B(2,0).
(2)I)A(0,1),B(√19,0)时,CA:x/(-3)+y=1,即x-3y+3=0,
B到AC的距离h=(√19+3)/√10,
|AC|=√10,
∴y=S△ABP=|AP|*h/2=|x-√10|*(√19+3)/(2√10),x>0且x≠√10.
ii)A(0,-4),B(2,0)时CA:x/(-3)+y/(-4)=1,即4x+3y+12=0,
B到AC的距离h=4,
|AC|=2√5,
仿上,y=2|x-2√5|,x>0,且x≠2√5.