In the diagram, ∠ PSR = 220°, ∠ SPQ = 58° and ∠ PQR =
MATHEMATICS
WAEC 2010
In the diagram, ∠ PSR = 220°, ∠ SPQ = 58° and ∠ PQR = 41°. Calculate the obtuse angle QRS.

- A. 90°
- B. 100°
- C. 121°
- D. 60°
Correct Answer: C. 121°
Explanation
Joining SQ. In \(\bigtriangleup\) SPQ,
(22o + a) + 55o + (41o + b) = 180o
121o + a + b = 180o
a + b = 180 - 121
a + b = 59o.....(1)
In \(\bigtriangleup\) SRPQ; R + a + b = 180o
R + 59o = 180o
(in (1), a + b = 59o)
R = 180 - 59
R = 121o
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