Which of the following is/are not the interior angle(s) of a regular polygon? I.108° II....
MATHEMATICS
WAEC 2003
Which of the following is/are not the interior angle(s) of a regular polygon? I.108° II. 116° III. 120°
- A. I only
- B. II only
- C. III only
- D. I and III only
Correct Answer: B. II only
Explanation
Using the formula, \((n - 2) \times 180°\) to get the sum of the interior angles. Then we can have
\((n - 2) \times 180° = 108n\) ... (1)
\((n - 2) \times 180° = 116n\) ... (2)
\((n - 2) \times 180° = 120n\) ... (3)
Solving the above given equations, where n is not a positive integer then that angle is not the interior for a regular polygon.
(1): \(180n - 360 = 108n \implies 72n = 360\)
\(n = 5\) (regular pentagon)
(2): \(180n - 360 = 116n \implies 64n = 360\)
\(n = 5.625\)
(3): \(180n - 360 = 120n \implies 60n = 360\)
\(n = 6\) (regular hexagon)
Hence, 116° is not an angle of a regular polygon.
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