C(a,b)
C∈[AB]
AC/CB=AB/AC
AC²=CB·AB
(a,b-4)²=(4,-4)(4a,-b)
(a²,(b-4)²)=(16a ,4b)
a²=16a (b-4)²=4b
a²-16a=0 b²-8b+16=4b
a(a-16)=0 b²-12b+16=0
a1=0 d=1
a2=16 e=-12
f=16
Δ=e²-4df=(-12)²-4·1·16=144-64=80
b1=(-e+√Δ)/2d=(12+√80)/2=(12+4√5)/2
b1 =6+2√5
b2=(-e-√Δ)/2d=(12-4√5)/2=6-2√5
a-b=0-(6+2√5)=-6-2√5
a-b=0-(6-2√5)=-6+2√5
a-b=16-(6+2√5)=10-2√5
a-b=16-(6-2√5)=10+2√5
