a level factorisation

Well using factor theorem, which I assume you did, you find that f(-2)=0, which shows that (x+2) is a factor.

You should be able to go from there.

What was your working out to get the incorrect answer?

i did f(0.5) instead

Ok, that is fine. 0.5=1/2

Using factor theorem, if f(1/2)=0, (2x-1) is a factor.

How did you get (2x-10)?

i did f(0.5) instead

that will tell you 2x - 1 is a factor, (since 0.5 = 1/2)

you can easily check your answer by partially multiplying out the brackets to check you get the same eqn you start with. the constants should make 10, yours make -80

now im confused can you show me how you would do it?

now im confused can you show me how you would do it?

Which bit are you confused with? You can find the first factor, and use polynomial division to find the other two.

The three factors that you found are not correct. You can tell this:

(x-a)(x-b)(x-c)=Ax^3+Bx^2+Cx+D, where D=(-a)(-b)(-c)

The constant in your cubic should be the product of the three constants in your factors.

i did the long division thing with (x-5) and got 2x^2 +3x - 2

is that right?

Yes. Factorise the quadratic and you will get the other two factors

(2x-1) (x+2) thats what i got... but theres no (x-5)

(x-5) is what you divided the original cubic by, so it is a factor