Chapter 2: Problem 14
Find the number of sides that a polygon has if the sum of the measures of its interior angles is: a) \(1980^{\circ}\) b) \(2340^{\circ}\)
Short Answer
Expert verified
(a) 13 sides; (b) 15 sides
Step by step solution
01
Use the formula for the sum of interior angles
The sum of the interior angles of a polygon with n sides is given by the formula \( (n-2) \times 180^{\circ} \). We will use this formula to find n for both (a) and (b).
02
Solve for n using equation for (a)
We know that the sum of the interior angles is \(1980^{\circ}\). Set up the equation: \((n-2) \times 180^{\circ} = 1980^{\circ}\).
03
Simplify and solve equation for (a)
Divide both sides by \(180\): \(n-2 = \frac{1980}{180}\). Simplify the right side to get \(n-2 = 11\). Add 2 to both sides to get \(n = 13\).
04
Solve for n using equation for (b)
The sum of the interior angles is given as \(2340^{\circ}\). Set up the equation: \((n-2) \times 180^{\circ} = 2340^{\circ}\).
05
Simplify and solve equation for (b)
Divide both sides by \(180\): \(n-2 = \frac{2340}{180}\). Simplify the right side to get \(n-2 = 13\). Add 2 to both sides to get \(n = 15\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Interior Angles
Interior angles are a fundamental concept in geometry, particularly when it comes to understanding polygons. These angles are formed where two sides of a polygon meet. For any given polygon, the interior angle at any vertex is the angle formed inside the shape.
- In a triangle, which is the simplest polygon, the interior angles add up to \(180^{\circ}\).
- As the number of sides increases, the sum of the interior angles also increases.
Sum of Interior Angles Formula
The formula for calculating the sum of the interior angles of a polygon is \((n-2) \times 180^{\circ}\), where \(n\) represents the number of sides of the polygon. This formula is derived from the concept that any polygon can be divided into triangles.
Here’s why this formula works:
Here’s why this formula works:
- Each triangle has a sum of angles that is \(180^{\circ}\).
- By dividing a polygon into triangles, we know there are \((n-2)\) triangles.
- As a result, the sum of the interior angles can be calculated by multiplying the number of triangles by \(180^{\circ}\).
Geometry Problem Solving
Problem-solving in geometry often requires a logical and methodical approach, especially when dealing with shapes and angles. For instance, if you are asked to find the number of sides of a polygon based on the sum of its interior angles, you would follow these steps:
- First, use the sum of interior angles formula \((n-2) \times 180^{\circ} = \text{Sum of angles}\).
- Rearrange the formula to solve for \(n\): \(n = \left( \frac{\text{Sum of angles}}{180} \right) + 2\).
- Substitute the given sum of interior angles into the formula and perform the calculation.