Question 15

Factorise 21-9x

The factored form would be 3 (7-3x).

The GCF of these two is 3; that is the largest number either of them can be divided by, and they do not have a variable in common. This gives us:

3 ()

21/3 = 7, so we have:

3 (7)

9x/3 = 3x, which gives us

3 (7-3x)