Question 126422
{{{3x^2 + 4x - 15}}}
{{{(3x - 5)(x + 3)}}}
I do this just by trying factors of 15 and 
moving the factors anf the + and - signs
around until it works
If the equation were {{{3x^2 + 44x - 15}}}
I would need big numbers, so I'd try 15 and 1 for
factors of 15
{{{(3x - 1)(x + 15)}}} works 
The more you play with them, the easier they get