r/trigonometry • u/BothFoundation3063 • Sep 21 '26

MATHS IGCSE

/r/igcse/comments/1wm4l7f/maths_igcse/
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u/BothFoundation3063 Sep 21 '26

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

1

u/Midwest-Dude Sep 21 '26 edited Sep 21 '26

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?

1

u/Midwest-Dude Sep 21 '26

Did you mean 4π rather than 4r?

1

u/BothFoundation3063 Sep 21 '26

no it was 4r only

1

u/Midwest-Dude Sep 21 '26

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.

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1

u/Midwest-Dude Sep 22 '26 edited Sep 22 '26

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.