This week in precalc 11, I continued learning about the connection between graphing and quadratic equations. One thing specifically that I learned about was how to plot the vertex on a graph, when given a quadratic equation. The “parent function” is like the original graph. It is created from the equation y=x². For this graph, the vertex is at the coordinates (0,0). This is what the parent function graph looks like:

When graphing an equation different than y=x², there are a few ways to find the coordinates of the vertex. First, see if there is a last number (without a variable) in the equation. This tells you where the vertex will be on the y-axis. If the number is positive, move the vertex upwards (the amount of spaces the number says). If it is negative, move down. As you can see below, the parabola is still the same shape and size as the parent function, just shifted in a different direction. Here are some examples:

y = x² + 2

y = x² – 7

If there is a number either added or subtracted from the x, this tells you where the vertex is on the x-axis. If the number is positive, move the vertex to the left. If it is negative, move to the right. Here are some examples:

y = (x + 1)²

y = (x – 3)²

Finally, these two things can be combined in an equation, so the vertex has coordinates that do not include zero. Here are a few more examples:

y = (x – 3)² + 4

y = (x – 1)² + 1