y=x^2-4x+k=(x-2)^2+k-4
x=2,y=k-4
y=-4x-1
k-4=-4*2-1
k=-5
A(2,-9)
y=x^2-4x-1
y=0
x^2-4x-9=0
|xB-xC|=2√13
s=(1/2)**9*2√13=9√13