 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 […] Example 1 Find the equation of the quadratic graph. \begin{align} \displaystyle y &= a(x+2)(x+1) \\ 2 &= a(0+2)(0+1) &\text{substitute }(0,2)\\ 2 &= 2a \\ a &= 1 \\ y &= 1(x+2)(x+1) \\ \therefore y &= x^2+3x+2 \\ \end{align} Example 2 Find the equation of the quadratic graph. \begin{align} \displaystyle y &= a(x+1)^2 […] # Quadratic Graphs by Completing the Square 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 […] # Axis of Symmetry of Quadratic Graphs The equation of the axis of symmetry of y=ax^2+bx+c is x=-\dfrac{b}{2a}. Example 1 Find the equation of the axis of symmetry of y=x^2+4x-2. \( \begin{align} \displaystyle x &= -\dfrac{b}{2a} \\ &= -\dfrac{4}{2 \times 1} \\ \therefore x &= -2 \\ \end{align} Example 2 Find the equation of the axis of symmetry of $y=-2x^2-12x+3$. […] # X-intercepts Y-intercepts x-intercepts when y=0 y-intercepts when x=0 Example 1 Sketch the graphs of y=x^2+x-2 by stating x- and y-intercepts. x-intercepts when y=0 \( \begin{align} \displaystyle x^2+x-2 &= 0 \\ (x+2)(x-1) &= 0 \\ x &= -2, 1 \\ \end{align} $y$-intercepts when $x=0$ \begin{align} \displaystyle y &= 0^2+0-2 \\ &= -2 \\ \end{align} Example […] # 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 […] 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 […]