x^2-4x+4=y
y=ax-2a-10
x^2-4ax+8a+40-4x+4=0
x^2-4(a+1)+8a+44
16(a+1)^2-4(8a+44)=0
(a+1)^2-(2a+11)=0
a^2=0
a=+-根号10