Trigonometric Confusion?

Mathegocart · 2018-09-25 12:20:14

Hello amiable users of this forum,

lately I have been facing a conundrum that was present on my math test.

The question asked me to solve a triangle ABC given that

<B = 38 deg

b = 15 miles

c = 27 miles

.. and to list all sides and angles, with explicit blanks for these sides and angles.

I then set up the corresponding Law Of Sines equation:

This then provides us with..

But sin(c)'s range is from -1 to 1. Am I making a mistake? Could it be a typo?

Thank you,

Mathegocart

Bob · 2018-09-25 19:38:21

hi Mathegocart

No error. No triangle can be made with those measurements. Try it yourself. Draw AB = 27 (may need to scale down) and angle B = 38. You don't know how long to make BC so just continue the line for some distance. Set a compass to a radius of AC = 15 and try to intersect BC. This fails. The shortest distance from A to BC is about 18.

Bob

Mathegocart · 2018-09-25 22:22:03

bob bundy wrote:

hi Mathegocart
No error. No triangle can be made with those measurements. Try it yourself. Draw AB = 27 (may need to scale down) and angle B = 38. You don't know how long to make BC so just continue the line for some distance. Set a compass to a radius of AC = 15 and try to intersect BC. This fails. The shortest distance from A to BC is about 18.
Bob

Do you think they made a typo? It was 6 points..

Bob · 2018-09-26 19:20:45

hi Mathegocart

Typos can creep into questions. In the UK the national exams are, nowadays, subject to a load of checking but question errors still get in sometimes. [eg. https://www.independent.co.uk/news/educ … 27141.html ]

Or maybe it was intended to test if you are aware that sometimes a calculation cannot be completed. If I was going to do this I would word my questions (have to be several) "Work out all the missing side lengths and angles in these triangles. If you think a triangle cannot exist explain why." Something like that would be reasonable if it was included like that as part of the assessment. If it was a single question on the topic, and you have copied it correctly**, then it looks like a serious error. What was the test?

Bob

** If the numbers are swapped around then it is possible for example.

Mathegocart · 2018-09-26 23:08:08

bob bundy wrote:

hi Mathegocart
Typos can creep into questions. In the UK the national exams are, nowadays, subject to a load of checking but question errors still get in sometimes. [eg. https://www.independent.co.uk/news/educ … 27141.html ]
Or maybe it was intended to test if you are aware that sometimes a calculation cannot be completed. If I was going to do this I would word my questions (have to be several) "Work out all the missing side lengths and angles in these triangles. If you think a triangle cannot exist explain why." Something like that would be reasonable if it was included like that as part of the assessment. If it was a single question on the topic, and you have copied it correctly**, then it looks like a serious error. What was the test?
Bob
** If the numbers are swapped around then it is possible for example.

This peculiar question was on an unit test on Trigonometry, and the problem, as I recall, was not worded as ".. if you think a triangle cannot exist explain why." There were merely blanks corresponding to the missing sides and angles, with the instruction saying "solve the triangle."

Bob · 2018-09-27 19:16:47

It's very odd. You'll have to raise this with your teacher.

B

Math Is Fun Forum

#1 2018-09-25 12:20:14

Trigonometric Confusion?

#2 2018-09-25 19:38:21

Re: Trigonometric Confusion?

#3 2018-09-25 22:22:03

Re: Trigonometric Confusion?

#4 2018-09-26 19:20:45

Re: Trigonometric Confusion?

#5 2018-09-26 23:08:08

Re: Trigonometric Confusion?

#6 2018-09-27 19:16:47

Re: Trigonometric Confusion?

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