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

Mathegocart
Member
Registered: 2012-04-29
Posts: 1,960

Trigonometric Confusion?

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


The integral of hope is reality.
May bobbym have a wonderful time in the pearly gates of heaven.
He will be sorely missed.

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

bob bundy
Administrator
Registered: 2010-06-20
Posts: 8,416

Re: Trigonometric Confusion?

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


Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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

Mathegocart
Member
Registered: 2012-04-29
Posts: 1,960

Re: Trigonometric Confusion?

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..


The integral of hope is reality.
May bobbym have a wonderful time in the pearly gates of heaven.
He will be sorely missed.

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

bob bundy
Administrator
Registered: 2010-06-20
Posts: 8,416

Re: Trigonometric Confusion?

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.


Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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

Mathegocart
Member
Registered: 2012-04-29
Posts: 1,960

Re: Trigonometric Confusion?

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."


The integral of hope is reality.
May bobbym have a wonderful time in the pearly gates of heaven.
He will be sorely missed.

Offline

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

bob bundy
Administrator
Registered: 2010-06-20
Posts: 8,416

Re: Trigonometric Confusion?

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

B


Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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