MCQ practice · SSC General Mathematics Board questions · Chapter 6: Lines, Angles and Triangles
The bisectors of ∠E and ∠F of ΔDEF meet at the point O. If ∠D = 100°, what is ∠EOF?
Think it through first, then pick an option.
- a 140°
- b 100°
- c 80°
- d 50°
Answer and explanation
Correct answer: a 140°
∠EOF = 90° + ½∠D = 90° + 50° = 140°.
Why the other options are wrong
- b 100°: 100° is ∠D itself, not ∠EOF; the angle at O is 90° + ½∠D = 140°.
- c 80°: 80° is 180° − 100°, the value of ∠E + ∠F, not of ∠EOF.
- d 50°: 50° is only ½∠D; the formula adds 90° to it, giving 90° + 50° = 140°.
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