From 90a521de14e102aad1674b4e9b60e41062372504 Mon Sep 17 00:00:00 2001 From: Andrew Lorimer Date: Sun, 2 Dec 2018 14:27:44 +1100 Subject: [PATCH 1/1] add factorising notes for methods --- methods/polynomials.md | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) create mode 100644 methods/polynomials.md diff --git a/methods/polynomials.md b/methods/polynomials.md new file mode 100644 index 0000000..6fadf11 --- /dev/null +++ b/methods/polynomials.md @@ -0,0 +1,16 @@ +# Polynomials + +## Factorising + +#### Quadratics +**Quadratics:** $x^2 + bx + c = (x+m)(x+n)$ where $mn=c$, $m+n=b$ +**Difference of squares:** $a^2 - b=^2 = (a - b)(a + b)$ +**Perfect squares:** $a^2 \pm 2ab + b^2 = (a \pm b^2)$ +**Completing the square (monic):** $x^2+bx+c=(x+{b\over2})^2+c-{b^2\over4}$ +**Completing the square (non-monic):** $ax^2+bx+c=a(x-{b\over2a})^2+c-{b^2\over4a}$ +**Quadratic formula:** $x={{-b\pm\sqrt{b^2-4ac}}\over2a}$ where $\Delta=b^2-4ac$ + +#### Cubics +**Difference of cubes:** $a^3 - b^3 = (a-b)(a^2 + ab + b^2)$ +**Sum of cubes:** $a^3 + b^3 = (a+b)(a^2 - ab + b^2)$ +**Perfect cubes:** $a^3 \pm 3a^2b + 3ab^2 \pm b^3 = (a \pm b)^3$ -- 2.43.2