If tan θ = 7/24 for an acute angle θ in a right-angled triangle, find the exact value of cosec θ. (Answer should be an exact fraction.)

Difficulty: Easy

Correct Answer: 25/7

Explanation:


Introduction / Context:
This problem tests converting between trigonometric ratios using a right-triangle interpretation. When tan θ is given as a fraction, you can treat it as opposite/adjacent, find the hypotenuse using Pythagoras, and then compute sin θ and cosec θ.


Given Data / Assumptions:

  • tan θ = 7/24
  • θ is acute (0° < θ < 90°), so all trig ratios are positive.
  • Use a right triangle model.


Concept / Approach:
Interpret tan θ = opposite/adjacent = 7/24. Take opposite = 7 and adjacent = 24. Then hypotenuse = sqrt(7^2 + 24^2). Once you have hypotenuse, compute sin θ = opposite/hypotenuse, and cosec θ = 1/sin θ.


Step-by-Step Solution:

Let opposite side = 7 and adjacent side = 24. Compute hypotenuse: hyp = sqrt(7^2 + 24^2) = sqrt(49 + 576) = sqrt(625) = 25. Now sin θ = opposite/hypotenuse = 7/25. Therefore cosec θ = 1/sin θ = 1/(7/25) = 25/7.


Verification / Alternative check:
Check consistency: tan θ = 7/24 matches the triangle. Also, since hypotenuse is the largest side and θ is acute, sin θ must be less than 1 (7/25), so cosec θ must be greater than 1 (25/7), which is reasonable.


Why Other Options Are Wrong:

25/24 and 24/25 come from confusing sec/cos style ratios with cosec. 7/25 is sin θ, not cosec θ. 24/7 is cot θ, not cosec θ.


Common Pitfalls:
Swapping opposite and adjacent, or using hypotenuse incorrectly. Remember: cosec is the reciprocal of sin, not the reciprocal of tan.


Final Answer:
cosec θ = 25/7

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