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# Factorising watch

1. Can someone show me a method of how to factorise x^3-8
2. Well, a good place to begin is to ask yourself if you can see any values of x for which x^3-8 = 0.
3. Look for values of x^3 = 8
4. Solve or factorize?
5. Solving x^3 - 8 = 0 and factorising x^3 - 8 are nearly the same thing
6. A to an odd power minus B to an odd power has a standard factorisation.
7. (Original post by Srai)
x^3 - 8

= (x - 2)^3
No it isn't, unless x equals 2.
8. (Original post by stevencarrwork)
No it isn't, unless x equals 2.
Sorry, my excuse is that I haven't slept at all today.

to make up for myself, the method you need to factorise x^3 - 8

is the difference of two cubes.

i.e.

a^3 ± b^3 = (a ± b)(a^2 ∓ ab + b^2)

so..

x^3 - 8 = (x)^3 - (2)^3

(x-2)(x^2 + 2x + 4)

if you want test it.

x^3 + 2x^2 + 4x - 2x^2 - 4x - 8

= x^3 - 8

try x^3 + 27
9. (Original post by Srai)
Sorry, my excuse is that I haven't slept at all today.

to make up for myself, the method you need to factorise x^3 - 8

is the difference of two cubes.

i.e.

a^3 ± b^3 = (a ± b)(a^2 ∓ ab + b^2)

so..

x^3 - 8 = (x)^3 - (2)^3

(x-2)(x^2 + 2x + 4)

if you want test it.

x^3 + 2x^2 + 4x - 2x^2 - 4x - 8

= x^3 - 8

try x^3 + 27
thanks srai , i actually never knew you could have the difference of two cubes

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