can $\displaystyle 3x^2+2x-5$ be factorised?

Printable View

- Nov 22nd 2009, 08:44 AMdecoy808factorise
can $\displaystyle 3x^2+2x-5$ be factorised?

- Nov 22nd 2009, 08:51 AMskeeter
- Nov 22nd 2009, 09:01 AMRaoh
$\displaystyle (x-1)(3x+5)$

- Nov 22nd 2009, 09:11 AMRaoh
- Nov 22nd 2009, 09:17 AMukorov
split coefficient of $\displaystyle x^2$, ie. 3, into its factors 3x and 1x. also split the constant -5 into -1 and +5

you will find that:

3 x -1 = -3

1 x +5 = +5

putting these two products together you have (-3) + (+5) = (+2), which is the coefficient of x. however when you fill up the brackets with these factors you don't write (3x - 1)(x + 5). You write (3x + 5)(x - 1).