The interior angles of a pentagon are (2x + 5)°, (x + 20)°, x°, (3x
MATHEMATICS
WAEC 2009
The interior angles of a pentagon are (2x + 5)°, (x + 20)°, x°, (3x - 20)° and (x + 15)°. Find the value of x
- A. 80°
- B. 70°
- C. 65°
- D. 40°
Correct Answer: C. 65°
Explanation
(2x + 5)o + (xo + 20o) + x + (3x - 20)o + (x + 15)o = (n - 2) x 180
8n + 20 = (5 - 2) x 180
where n = 5(Pentagon)
8n + 20 = 3 x 180
8n + 20 = 540
8n = 540 - 20
8n = 520
x = 65°
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