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?

using the formula $$a^2-b^2=(a-b)(a+b)$$ we obtain
$$(x-1)^2-(x-5)^2=(x-1-x+5)(x-1+x-5)=4(2x-6)=8(x-3)$$
