Question

how we take common (k+1) from above eq.

Answer 1

I hope that this helps

Answer 2

=>4k3+18k2+23k+9/3

=>4k3+18k2+14k+9k+9/3

=>4k3+4k2+14k2+14k+9k+9/3

=>4k2(k+1)+14k(k+1)+9(k+1)/3

Now (k+1) is common factor..
then

=>(k+1)(4k2+14k+9)/3

hope it will help you..