y=(x+m)2+k
顶点坐标为M(1,-4);y=(x-1)^2-4=x^2-2x-3;
x1*x2=-3;x1+x2=2;(x1-x2)^2=(x1+x2)^2-4x1x2=4+12=16,
|x1-x2|=4,
S△MAB =1/2|x1-x2|*|-4|=8;
设P(X,Y),Y=X^2-2X-3;
S△PAB=1/2|x1-x2|*|Y|=2|X^2-2X-3|=10,
|X^2-2X-3|=5;
X^2-2X-3=±5;
X^2-2X-8=0;或X^2-2X+2=0;
X1=4;X2=-2;Y1=5;Y2=5;
X^2-2X+2=0;无实数解;P有两点可取,(4,5);(-2,5)