The formulas for perimeter and area are obviously useful for calculating the perimeter and area of plane figures, but they can also be used to find missing measurements.
Finding a missing measurement in plane figures consists of determining an unknown measurement in a figure when the area or the perimeter is known.
Simply apply a structured approach that takes advantage of the algebraic methods for solving equations. In other words, finding a missing measurement is the perfect meeting between the worlds of geometry and algebra!
A missing measurement can be isolated using either the formulas for the area or perimeter. It depends on the context of the situation. For solids, the missing measurements might be related to the volume. Please consult the concept sheet Missing Measurements in Solids if this is the case. In the concept sheets in this section, a variety of examples can be found which group together practically all the possible cases concerning plane figures:
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simple figures (rectangle, triangle, trapezoid, circle, etc.) or figures that can be decomposed;
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a single unknown value or several values related by an algebraic formula;
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problems that use one or two variables;
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first- and second-degree equations.
Knowing how to isolate a variable in a geometric formula or in any other equation is one of the most important skills a student needs to master to progress in mathematics, science, or any related subject. So, it is worthwhile to practice these skills often to become very comfortable using them.
Pour valider ta compréhension des mesures manquantes dans les figures planes de façon interactive, consulte la MiniRécup suivante :
