Answer
(r-4)(r+1)
Work Step by Step
Given the polynomial
$r^{2}$ - 3r - 4
*** We break of the middle term into two factors that add to give -3 and multiply to give -4. The two numbers are -4 and +1.
$r^{2}$ - 4r +1r - 4
We take the GCD of the first two and the GDC of the last two terms.
r(r-4) +1(r-4)
We take (r-4) and factor it out which gives us.
(r-4)(r+1)