Before watching this video, make sure you're familiar with the formulas for the perimeter and area of plane figures. You should also be familiar with general methods of solving equations, such as the balancing equations method. These different notions are essential when you're looking for a missing measurement in plane figures.
The following table is a summary of various formulas for the perimeter and area of plane figures:
To find a missing measurement in plane figures, you must apply one of the general methods for solving equations to the formula used in the problem. This could be a perimeter or area formula.
Here's an example of the steps to follow when you encounter a problem that requires you to find a missing measurement in plane figures:
If the perimeter of an octagon measures 76.8 mm, what is the measure of one of its sides?
|
Number of sides: |8| Measure of one side: |\color{#3A9A38}{s}| Perimeter: |76.8\ \text{mm}| |
|---|---|
|
||P=n\color{#3A9A38}{s}|| |
|
||76.8=8 \color{#3A9A38}{s}|| |
|
||\begin{align}\dfrac{76.8}{\color{#EC0000}{8}}&=\dfrac{8\times\color{#3A9A38}{s}}{\color{#EC0000}{8}}\\9.6&=\color{#3A9A38}{s}\end{align}|| |
| Answer: One side of the octagon measures |9.6\ \text{mm}.| | |