Substituting x=-4 and y=0 gives: -4k+3=0,
∴k=,
The analytical formula of the straight line is y=x+3,
② It is known that the coordinate of point P is (1, m),
∴m=× 1+3=;
(2)∫PP′∨AC,
△PP′D∽△ACD,
= =, that is =,
∴a=;
(3) When the point p is in the first quadrant,
1) If ∠ AP ′ c = 90, P ′ a = P ′ c (as shown in figure 1).
Passing point p' is the axis of P'H⊥x at point H.
∴pp′=ch=ah=p′h=ac.
∴2a=(a+4),
∴a=,
2) If ∠ p ′ ac = 90 and p ′ a = c,
Then PP'= AC,
∴2a=a+4,
∴a=4,
3) If ∠ p ′ ca = 90,
Then points p' and p are in the first quadrant, which contradicts the condition.
∴△ p ′ ca cannot be an isosceles right triangle with C as the right vertex.
∴a All values that meet the conditions are a=4 or.