How to factorise $(x-1)^2 - (x-5)^2$? My attempt: 
$a = (x-1)$ 
$c = (x-5)$
$a^2 - c^2$
which is equal to: 
$$((x-1) - (x-5))((x-1)+(x-5))$$
But the correct answer is : 
$8(x-3)$
Can you explain, please?


$${ \left( x-1 \right)  }^{ 2 }-{ \left( x-5 \right)  }^{ 2 }=\left( x-1-x+5 \right) \left( x-1+x-5 \right) =4\left( 2x-6 \right) =8\left( x-3 \right)  $$

