a)
y=mx+1 ---(1)
y= -mx+m ---(2)
Combine (1)&(2),
mx+1 = -mx+m
2mx = m-1
x = (m-1)/2m ---(3)
Put (3) into (1),
y=[m(m-1)/2m] +1 = [(m-1)/2] +1 = (m+1)/2
Coor. of P = [(m-1)/2m , (m+1)/2]
b)
若p是y軸上的一點, set x=0 and
(m-1)/2m = 0 => m=1
i.e. Coor. of P = [0 , 1]