i've now got the question: factorise: $\displaystyle x^3 - a^3$ but i don't know what to do when its only letters involved without the help of any numbers, could someone show me how to do it this way?

thanks

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- Sep 13th 2009, 08:46 AMmarkfactorising
i've now got the question: factorise: $\displaystyle x^3 - a^3$ but i don't know what to do when its only letters involved without the help of any numbers, could someone show me how to do it this way?

thanks - Sep 13th 2009, 08:49 AMe^(i*pi)
- Sep 13th 2009, 09:06 AMmark
i tried that formula out but it didn't seem to work. say i put p = 4 and q = 2 the equation would be $\displaystyle 4^3 - 2^3 = 64 - 8 = 56$ so then it would be $\displaystyle (4 - 2)(4^2 + 4(-2) + -2^2)$ which then leads to $\displaystyle 2(16 - 8 + 4)$ then 32 - 16 + 8 = 24 ,so obviously not 56. whats gone wrong here?

- Sep 13th 2009, 09:08 AMe^(i*pi)
- Sep 13th 2009, 09:10 AMmark
ah i see thanks, silly mistake there