Question

How to factor: k^2-13k+40

Answer 1

$k^2-13k+40\\\\------------------------\\\\-13=-5+(-8)\\\\40=(-5)\cdot(-8)\\\\-------------------------\\\\k^2-13k+40=(k-5)(k-8)$

Answer 2

$k^2-13k+40=k^2-5k-8k+40=k(k-5)-8(k-5)=\\\\=(k-5)(k-8)$