What you need to know
This topic includes graphs which are not straight.
These include, quadratic graphs, cubic graphs, reciprocal graphs and exponential graphs.
You will also be required to identify and plot these graphs.
You need to be happy with the following topics:
– Drawing straight line graphs revision
Quadratic graphs
Quadratic graphs have the general form
\textcolor{red}{a}x^2 + \textcolor{limegreen}{b}x+\textcolor{blue}{c}
These form a \bigcup or \bigcap shape, examples are shown below:
Note: \textcolor{limegreen}{b} and \textcolor{blue}{c} can be zero, as is the case with y=x^2
Cubic Graphs
Cubic graphs have the general form
\textcolor{red}{a}x^3 + \textcolor{limegreen}{b}x^2+\textcolor{blue}{c}x +\textcolor{yellow}{d}
These form S shape in the middle.
Note: Sometimes this S can be flat.
Reciprocal graphs
Reciprocal functions have the general equation:
y = \dfrac{\textcolor{red}{k}}{x}
e.g:
y = \dfrac{\textcolor{red}{1}}{k}
Exponential Graphs
Exponential functions have the general equation:
y = \textcolor{blue}{k}^x
e.g:
y = \textcolor{blue}{3}^x
Example: Plotting quadratics
Plot the following quadratic equation:
y=x^2-x-5
First draw a table of coordinates from x=-2 to x=3, then use the values to plot the graph between these values of x.
Step 1: Draw a table for the values of x between -2 and 3.
Step 2: Next we need to substitute our value of x into the equation to get the corresponding y value.
E.g: When x=\textcolor{red}{-2}, we get
y=(\textcolor{red}{-2})^2-(\textcolor{red}{-2})-5=4+2-5= \textcolor{blue}{1}.
Step 3: We then continue this process for all other values of x
Step 4: Then from the table we get coordinates to plot. e.g. (\textcolor{red}{-2}, \textcolor{blue}{1})
Once plotted, we join all the points with a smooth curve giving the following.
Example: Plotting harder graphs
Using the equation y=x^3-2x^2, draw a table of coordinates from x=-1 to x=3. Use the values to plot the graph between these x values.
Step 1: Draw a table of the coordinates for x from -1 to 3
Step 2: Next we need to substitute our value of x into the equation to get the corresponding y value.
For example, for x=\textcolor{red}{1}, we get
y=\textcolor{red}{1}^3-2(\textcolor{red}{1})^2=\textcolor{blue}{-1}.
Step 3: We then continue this process for all other values of x
Step 4: Then from the table we get coordinates to plot. e.g. (\textcolor{red}{1}, \textcolor{blue}{-1})
Once plotted, we join all the points with a smooth curve giving the following.
Example Questions
1) Using the equation y=x^2+4x-9, complete the table of coordinates below. Use these coordinates to plot the graph between x=-5 and x=2.
We will complete this table by substituting in the values of x to get the missing values of y. For example, when x=2,
y=(-4)^2+4(-4)-9=16-16-9=-9
Continuing this with the rest of the x values, we get the completed table below.
Then, plotting these coordinates on a pair of axes and joining them with a curve, we get the graph below.
2) Using the equation y=x^3+3x^2-4, complete the table of coordinates below. Use these coordinates to plot the graph between x=-4 and x=1.
We will complete this table by substituting in the values of x to get the missing values of y. For example, when x=-2,
y=(-2)^3+3(-2)^2-4=-8+12-4=0
Continuing this with the rest of the x values, we get the completed table below.
Then, plotting these points on a pair of axes and joining them with a curve, we get the graph below.
3) (HIGHER ONLY) Using the equation y=(0.2)^x, complete the table of coordinates below. Use these coordinates to plot the graph between x=-1 and x=4.
We will complete this table by substituting in the values of x to get the missing values of y. For example, when x=2,
y=(0.2)^2=0.04
Continuing this with the rest of the x values, we get the completed table below.
Then, plotting these points on a pair of axes (to the best of your ability – when some of them are so small they’re naturally going to practically end up on the x-axis) and joining them with a curve, we get the graph below.
4) Using the equation y=3^x, draw a table of coordinates from x=-3 to x=2.
Use the values to plot the graph between these x values.
We draw this table by substituting the x values into the equation. For example, for x=1, we get
y=3^1=3.
Carrying this on with the rest of the numbers, we get the table above. Then, plotting these points and joining them with a curve, we get the graph to the right.
The exponential graph also has an asymptote along the x-axis. Its shape varies very little, except that when the base of the exponential (here, the function is 3^x so the base is 3) is a number between 0 and 1, the shape of the graph is a mirror image of this one. Specifically, a reflection in the y-axis.
5) Using the equation y=\frac{1}{x}, draw a table of coordinates from x=1 to x=5. Use the values to plot the graph between x=0 and x=5.
We draw this table by substituting the x values into the equation. For example, for x=2, we get
y=\frac{1}{2}=0.5.
Worksheets and Exam Questions
(NEW) Plotting Quadratics and Harder Graphs Exam Style Questions
Level 5-6Drawing Quadratic Graphs
Level 4-5Plotting Quadratics and Harder Graphs
Level 4-5Plotting Harder graphs
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