How do you factor this?
4x^2 - 21x - 18?
well, the factors of 18 are 1,2,3,6,9,18
The -21 in the middle makes me think that 2,9 will be likely, so
(4x+9)(x-2) gives +x nope
(2x+9)(2x-2) gives +14
Hmmm. That pesky 4. So,
(4x+3)(x-6) : -21x YAY!