Factorize the following:

The greatest common factor of the terms 5x and 15x2 of the expression 5x - 15x2 is 5x. 

Now,

$5 x=5 x \times 1$

and

$-15 x^{2}=5 x \times-3 x$

Hence, the expression 5x - 15x2 can be factorised as 5x(1 - 3x)​.