1# Polynomials 2 3## Factorising 4 5#### Quadratics 6**Quadratics:** $x^2 + bx + c = (x+m)(x+n)$ where $mn=c$, $m+n=b$ 7**Difference of squares:** $a^2 - b^2 = (a - b)(a + b)$ 8**Perfect squares:** $a^2 \pm 2ab + b^2 = (a \pm b^2)$ 9**Completing the square (monic):** $x^2+bx+c=(x+{b\over2})^2+c-{b^2\over4}$ 10**Completing the square (non-monic):** $ax^2+bx+c=a(x-{b\over2a})^2+c-{b^2\over4a}$ 11**Quadratic formula:** $x={{-b\pm\sqrt{b^2-4ac}}\over2a}$ where $\Delta=b^2-4ac$ (if $\Delta$ is a perfect square, rational roots) 12 13#### Cubics 14**Difference of cubes:** $a^3 - b^3 = (a-b)(a^2 + ab + b^2)$ 15**Sum of cubes:** $a^3 + b^3 = (a+b)(a^2 - ab + b^2)$ 16**Perfect cubes:** $a^3 \pm 3a^2b + 3ab^2 \pm b^3 = (a \pm b)^3$ 17 18## Linear and quadratic graphs 19 20### Forms of linear equations 21 22$y=mx+c$ where $m$ is gradient and $c$ is $y$-intercept 23${x \over a} + {y \over b}=1$ where $m$ is gradient and $(x_1, y_1)$ lies on the graph 24$y-y_1 = m(x-x_1)$ where $(a,0)$ and $(0,b)$ are $x$- and $y$-intercepts 25 26## Line properties 27 28Parallel lines: $m_1 = m_2$ 29Perpendicular lines: $m_1 \times m_2 = -1$ 30Distance: $\vec{AB} = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$ 31 32 33## Cubic graphs 34 35$$y=a(x-b)^3 + c$$ 36 37- $m=0$ at *stationary point of inflection* 38- in form $y=(x-a)^2(x-b)$, local max at $x=a$, local min at $x=b$ 39- in form $y=a(x-b)(x-c)(x-d)$: $x$-intercepts at $b, c, d$ 40 41 42## Quartic graphs 43 44### Forms of quadratic equations 45$y=ax^4$ 46$y=a(x-b)(x-c)(x-d)(x-e)$ 47$y=ax^4+cd^2 (c \ge 0)$ 48$y=ax^2(x-b)(x-c)$ 49$y=a(x-b)^2(x-c)^2$ 50$y=a(x-b)(x-c)^3$ 51 52## Literal equations 53 54Equations with multiple pronumerals. Solutions are expressed in terms of pronumerals (parameters) 55 56## Simultaneous equations (linear) 57 58- **Unique solution** - lines intersect at point 59- **Infinitely many solutions** - lines are equal 60- **No solution** - lines are parallel 61 62 63 64### Solving $\begin{cases}px + qy = a \\ rx + sy = b\end{cases}$ for one, infinite and no solutions 65 66where all coefficients are known except for one, and $a, b$ are known 67 681. Write as matrices: $\begin{bmatrix}p & q \\ r & s \end{bmatrix} 69\begin{bmatrix} x \\ y \end{bmatrix} 70 = 71\begin{bmatrix} a \\ b \end{bmatrix}$ 722. Find determinant of first matrix: $\Delta = ps-qr$ 733. Let $\Delta = 0$ for number of solutions $\ne 1$ 74 or let $\Delta \ne 0$ for one unique solution. 754. Solve determinant equation to find variable 76- *--- for infinite/no solutions: ---* 775. Substitute variable into both original equations 786. Rearrange equations so that LHS of each is the same 797. If $\text{RHS}(1) = \text{RHS}(2)$, lines are coincident (infinite solutions) 80 If $\text{RHS}(1) \ne \text{RHS}(2)$, lines are parallel (no solutions) 81 82Or use Matrix -> `det` on CAS. 83 84### Solving $\begin{cases}a_1 x + b_1 y + c_1 z = d_1 \\ 85a_2 x + b_2 y + c_2 z = d_2 \\ 86a_3 x + b_3 y + c_3 z = d_3\end{cases}$ 87 88- Use elimination 89- Generate two new equations with only two variables 90- Rearrange & solve 91- Substitute one variable into another equation to find another variable 92- etc.