Factorise the following: 21x(squared)-35x

The question is asking us to factorise, this means put the equation into a simplified bracket. The first step is to find the highest common factor (HCF), the HCF must be a factor of 21x² as well as -35x. I can see that x is a common factor so lets take x out of the equation: x(21x-35). Looking back into the bracket, I can see that 7 is a factor of 21x and -35. So lets take 7 out of the bracket, this makes the equation: 7x(3x-5). I can now see that the equation has been simplified because 3 is a prime number.
We can check our answers by expanding the bracket: 7x(3x) -7x(5) = 21x² -35x therefore our answer is correct.