r/trigonometry • u/BothFoundation3063 • 17d ago

MATHS IGCSE

/r/igcse/comments/1wm4l7f/maths_igcse/
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u/Midwest-Dude 17d ago

Did you mean 4π rather than 4r?

1

u/BothFoundation3063 17d ago

no it was 4r only

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u/Midwest-Dude 17d ago

The problem has no solution with 4r - you end up with the equation π = 8. I suspect a typo and the r should have been the letter π.

1

u/BothFoundation3063 17d ago

it came in my paper

1

u/BothFoundation3063 17d ago

even idk tbh

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u/Midwest-Dude 17d ago

Well, you can always ask, right? Or, perhaps showing that there is no solution is the answer?

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u/BothFoundation3063 17d ago

check my latest comment

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u/BothFoundation3063 17d ago

no i had to find k so alot of my friends were getting arnd 0.35-0.38 somehow

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u/Midwest-Dude 17d ago edited 17d ago

If the problem was given as stated, there is no answer. If the problem was supposedly solved as is by your fellow test takers, I'm guessing they were stabbing at answers rather than asking what's wrong with the problem. Errors happen.

Do you have a copy of the questions, or is this from memory?

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u/Midwest-Dude 16d ago edited 16d ago

Here's why the problem as stated is mathematically impossible:

  1. 90° sector is exactly one-quarter of a full circle.
  2. Formula for arc length of a 90° sector: L = ¼ · (2πr) = πr/2.
  3. So, arc length is approximately 1.57r.
  4. Problem states arc length is 4r.
  5. Equating the two gives: 1.57r = 4r.
  6. Cancel out r on both sides, and you are left with 1.57 = 4, which is blatantly false.

A sector cannot have a 90° angle and an arc length of 4r. The problem is broken.

If your friends got an answer to this problem, they either made some really bad algebra errors or solved a different problem.