Geometry and TrigonometryVery hardSine of a complementary angle
Geometry and Trigonometry practice question
For an acute angle B, cos B = 5/13. What is the value of sin(90° − B)?
Answer: 5/13
The sine of an angle equals the cosine of its complement: sin(90° − B) = cos B = 5/13.
Common wrong answers
- If you answered 12/13
- 12/13 is sin B (the other leg over the hypotenuse), not sin of the complement.
- If you answered 5/12
- 5/12 is a tangent ratio, not a sine.
- If you answered 13/5
- 13/5 is the reciprocal of cos B, which is not a sine of anything.
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