Factorising Quadratics

General form: x^2 + bx + c
- Find two numbers that:
  - Multiply to make c
  - Add to make b
- Example: x^2 + 9x + 20 = (x + 4)(x + 5)
  - 4\cdot5=20
  - 4 + 5 = 9
Example: p^2 + 9p + 14 = (p + 7)(p + 2)
- Factors of +14 are 1 × 14 and 2 × 7
- +2 and +7 add up to +9
Example: a^2 + 9a - 22 = (a + 11)(a - 2)
- Factors of -22 are one positive, one negative
- Factors of 22 are 1 × 22 and 2 × 11
- +11 and -2 add up to +9

General shape: a^2 - b^2 = (a + b)(a - b)
- Example: q^2 - 25 = (q - 5)(q + 5)
  - Factors of -25 are one positive, one negative
  - Factors of 25 are 1 × 25 and 5 × 5
  - There are zero q so we need +5 and -5