MCQ practice · SSC General Mathematics Board questions · Chapter 9: Trigonometric Ratio
If sin 5A = cos 5A, what is A?
Think it through first, then pick an option.
- a 45°
- b 30°
- c 9°
- d 6°
Answer and explanation
Correct answer: c 9°
sin x = cos x at x = 45°; 5A = 45° so A = 9°.
Why the other options are wrong
- a 45°: 45° is the value of 5A, not of A; A = 45°/5 = 9°.
- b 30°: A = 30° gives 5A = 150°, where sin 150° and cos 150° are not equal.
- d 6°: A = 6° gives 5A = 30°; sin 30° = 1/2 but cos 30° = √3/2.
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