For a number to be a factor of a polynomial, the polynomial must equal 0 when the said number is substituted into the equation in place of x.

The factor of this polynomial is x = 20; when we put 20 into the expression, we get 2(20) - (20) - 20, giving us an overall answer of 0. This is because as there is no sign in between the 2 and the (20), we can assume that we are to multiply them together, giving us 40 - (20) - 20, which we know equals 0.

We can work out that the answer is 20 by making our expression X2 - x - 20 equal 0.

Firstly, though, we must rewrite the expression, making it more easily read and therefore more easily solved. By doing this, and by making it equal 0, we gain an equation of 2x - x - 20 = 0.

Now we must take the - 20 over the equals sign, giving us 2x - x = 20. The change in sign (from a minus to an addition) is because when we take a variable or numerical value over the equals sign, it swaps its sign to its opposite; a multiplication to a division, a minus to an addition.

All that is left to do now is to factorise the left hand side of our equation. Because x is the common factor in 2x - x, we can bring x outside of our bracket, giving us x( ) = 20.

Now all we have to do is think about which numbers we need to go into the bracket that, when multiplied with x, gives us 2x - x, which we can easily see is x(2 - 1).

When 1 is taken from 2 we get an answer of 1 which, when multiplied by our x, gives us 1x = 20 or, as more commonly written x = 20, our final answer.

The factor of this polynomial is x = 20; when we put 20 into the expression, we get 2(20) - (20) - 20, giving us an overall answer of 0. This is because as there is no sign in between the 2 and the (20), we can assume that we are to multiply them together, giving us 40 - (20) - 20, which we know equals 0.

We can work out that the answer is 20 by making our expression X2 - x - 20 equal 0.

Firstly, though, we must rewrite the expression, making it more easily read and therefore more easily solved. By doing this, and by making it equal 0, we gain an equation of 2x - x - 20 = 0.

Now we must take the - 20 over the equals sign, giving us 2x - x = 20. The change in sign (from a minus to an addition) is because when we take a variable or numerical value over the equals sign, it swaps its sign to its opposite; a multiplication to a division, a minus to an addition.

All that is left to do now is to factorise the left hand side of our equation. Because x is the common factor in 2x - x, we can bring x outside of our bracket, giving us x( ) = 20.

Now all we have to do is think about which numbers we need to go into the bracket that, when multiplied with x, gives us 2x - x, which we can easily see is x(2 - 1).

When 1 is taken from 2 we get an answer of 1 which, when multiplied by our x, gives us 1x = 20 or, as more commonly written x = 20, our final answer.