1) simple. Let y=a(x+ 1)(x-4) and bring in the coordinates of point C.

2) There are two situations. In the first case, when ∠ACP is a right angle, the point P is perpendicular to the Y axis of PM, and it is assumed that P(x0, y0).

From △AOC∽△PMC, the P-point coordinates are solved by similarity method.

When ∠PAC is a right angle, the intersection point A is the straight line l⊥x axis, the intersection point P is PH⊥l, and the intersection point C is CG⊥l, according to △PHA∽AGC.

3) simple, then mainly look for EF? =PE？ +PF？ Find the maximum value in the form of quadratic function, or set the coordinates of P point.