Consider the graphs of a quadratic function and a linear function on the same set of axes. cutting2 points of intersection $b^2-4ac \gt 0$ touching1 point of intersection $b^2-4ac = 0$ missingno points of intersection $b^2-4ac \lt 0$ In the graphs meet, the coordinates of the points of intersection of the graphs can be found […]

# Quadratic Graphs in Completed Square Form

$$y=(x-a)^2+b$$ Example 1 Draw the graph of $y=(x-1)^2+2$. The vertex is $(1,2)$ and the graph is concave up. Example 2 Draw the graph of $y=(x-1)^2-2$. The vertex is $(1,-2)$ and the graph is concave up. Example 3 Draw the graph of $y=(x+1)^2+2$. The vertex is $(-1,2)$ and the graph is concave up. Example 4 Draw […]

The process of finding the maximum or minimum value of a functions is called optimisation. For the quadratic function $y=ax^2+bx+c$, we have already seen that the vertex has $x$-coordinate $-\dfrac{b}{2a}$. $a>0$: the minimum value of $y$ occurs at $x=-\dfrac{b}{2a}$ $a<0$: the maximum value of $y$ occurs at $x=-\dfrac{b}{2a}$ There are many cases for which we […]

# Positive Definite Negative Definite

The Discriminant and the Quadratic Graph The discriminant of the quadratic equation $ax^2+bx+c=0$ is $\Delta = b^2-4ac$. We used the discriminant to determine the number of real roots of the quadratic equation. If they exist, these roots correspond to $x$-intercepts of the quadratic $y = ax^2+bx+c$. The discriminant tells us about the relationship between a […]

Not all quadratics factorise easily. For instance, $x^2+6x+2$ cannot be factorised by simple factorisation. In other words, we cannot write $x^2+6x+2$ in the form $(x-a)(x-b)$ where $a$ and $b$ are rational. An alternative way to solve this equation $x^2+6x+2$ is by completing the square. Equations of the form $ax^2+bx+c$ can be converted to the form […]