9x2-5x-10
This trinomial cannot be factored, so whenever you find
one like that in a set of problems, you simply write the
word "prime".
How to tell if a trinomial Ax2+Bx+C is prime:
Calculate B2-4AC = (-5)2-4(9)(-10) = 25+360 = 385.
This is not a perfect square, because the square root of
385 is 19.62141687..., not a whole number. So the trinomial
is prime, that is, it cannot be factored.
Edwin
