Once again, we will do it the long way so you can see what is involved.

In this case, we need 2n2 so we start with:

2n2 − 13n − 7 = (2n  ...   )(n  ...   )

Now we need 2 numbers that multiply to give −7 and the sum of the inner and outer products must be −13. Don't forget the 2 in the first bracket!

Possibility 1: −7 and 1

Multiply to give −7

2n2 − 13n − 7 = (2n − 7)(n + 1)

Outer product plus inner product:

(2n)(1) + (−7)(n) = 2n − 7n = −5n

This is not the correct answer.

Possibility 2: 7 and −1

This would give us

Outer product plus inner product:

(2n)(−1) + (7)(n) = −2n + 7n = 5n

Possibility 3: −1 and 7

2n2 − 13n − 7 = (2n − 1)(n + 7)

Outer product plus inner product:

(2n)(7) + (−1)(n) = 14nn = 13n

This is still not the correct answer.

Possibility 4: 1 and −7

2n2 − 13n − 7 = (2n + 1)(n − 7)

Outer product plus inner product:

(2n)(−7) + (1)(n) = −14n + n = −13n

This is the required answer, finally.

So

2n2 − 13n − 7 = (2n + 1)(n − 7)

I repeat, it won't always involve several steps like this. The more you do them, the easier and quicker they become (like most new skills).