Question: Get two points in a plane

In geom3d, i have equation a plane. Now i want to get two points A and B in the plane P and write the equation of the line which passing two point A, B. 

plane(P, 2*x + 2*y -z + 4=0,[x,y,z]):
f := (a,b,c) -> eval(lhs(Equation(P)), [x=a,y=b,z=c]): 
T:=f(-1,2, a):
eq:=solve(T=0,a): coordinates(point(A,-1,2,eq)):
eq1:=solve(L=0,b): coordinates(point(B,4,1,eq1)):
In this way, i must input coordinates(point(A,-1,2,eq)): by my hand. 
Is there another way? Please help me. Thank you very much.
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