Question

Factorise the following:

3x² – 15x – 18

Answer 1

To factorise the quadratic expression:

3x² – 15x – 18

Step 1: Look for a common factor.

All terms are divisible by 3:

3x² – 15x – 18

= 3(x² – 5x – 6)

Step 2: Factorise the quadratic inside the bracket.

We need two numbers that multiply to –6 and add up to –5.

These are –6 and 1:

x² – 5x – 6

= (x – 6) (x + 1)

Step 3: Combine with the common factor.

3x² – 15x – 18

= 3(x – 6) (x + 1)

3(x – 6) (x + 1)