# How do you factor x^2 + 3x -5x^2 - 15?

May 19, 2015

Please check the question?

$y = - 4 {x}^{2} + 3 x - 15.$

This trinomial can't be factored because D = b^2 - 4ac < 0.

The correct question should be: factor $y = {x}^{3} + 3 x - 5 {x}^{2} - 15.$
To factor, group the first term and the second term together:

$y = x \left({x}^{2} + 3\right) - 5 \left({x}^{2} + 3\right) = \left({x}^{2} + 3\right) \left(x - 5\right)$

Check by developing:$y = {x}^{3} - 5 {x}^{2} + 3 x - 15.$ OK