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maths trigonometry ambiguous sine rule help

I have completed these questions but I cannot access the answers, can someone who is good at maths check if its correct please:

state in each case if there is one or two possible solutions

In triangle LMN n=7.3, l=5.1 and angle L =41.1
my answer was two solutions, either 69 degrees or 28.9 degrees.

the 2nd question is triangle ABC, b=3.19, a=3.8 and angle A=72 degrees.
my answer is just one solution= 53 degrees

Any help greatly appreciated.
Original post by Rainbowpink1999x
I have completed these questions but I cannot access the answers, can someone who is good at maths check if its correct please:

state in each case if there is one or two possible solutions

In triangle LMN n=7.3, l=5.1 and angle L =41.1
my answer was two solutions, either 69 degrees or 28.9 degrees.

the 2nd question is triangle ABC, b=3.19, a=3.8 and angle A=72 degrees.
my answer is just one solution= 53 degrees

Any help greatly appreciated.

could you perhaps send a picture or screenshot of the question? When you label a side it should be 2 letters :smile:
Original post by philogrobized
could you perhaps send a picture or screenshot of the question? When you label a side it should be 2 letters :smile:

C4BBDA2E-7449-404D-A6BE-6EED18A25D08.jpeg Hopefully you can view this, thanks for the reply
Original post by Rainbowpink1999x
C4BBDA2E-7449-404D-A6BE-6EED18A25D08.jpeg Hopefully you can view this, thanks for the reply


Could you also perhaps attach your working out as I have an answer but it is different to yours :smile:
Reply 4
Original post by Rainbowpink1999x
C4BBDA2E-7449-404D-A6BE-6EED18A25D08.jpeg Hopefully you can view this, thanks for the reply

For a) the multiple values occur with one <90 and the other >90? A sketch usually helps.
https://www.mathsisfun.com/algebra/trig-sine-law.html
(edited 3 years ago)
Original post by philogrobized
Could you also perhaps attach your working out as I have an answer but it is different to yours :smile:

I’ll attach what I did in a second, although it’ll be super messy and probably wrong

Original post by mqb2766
For a) the multiple values occur with one <90 and the other >90? A sketch usually helps.
https://www.mathsisfun.com/algebra/trig-sine-law.html

Sorry I don’t really get it, so it has to be bigger than 90?
Reply 6
Original post by Rainbowpink1999x
I’ll attach what I did in a second, although it’ll be super messy and probably wrong


Sorry I don’t really get it, so it has to be bigger than 90?

The sin() must be the same. So one solution is acute, the other obtuse.
It's covered in the link.
Original post by Rainbowpink1999x
I’ll attach what I did in a second, although it’ll be super messy and probably wrong


Sorry I don’t really get it, so it has to be bigger than 90?

image.jpg
Original post by Rainbowpink1999x
image.jpg

image.jpgThis is for question b, thanks guys really appreciate the help, I’m a little baffled right now
Original post by Rainbowpink1999x
image.jpg

image.jpgThis is for question b, thanks guys really appreciate the help, I’m a little baffled right now
For b) assuming the numbers are right, what would the obtuse solution be? Why can it be neglected? Tbh. The initial sketch is important. Your 72 angle is far too small.
(edited 3 years ago)
Original post by Rainbowpink1999x
image.jpg


Original post by Rainbowpink1999x
image.jpg


I agree with your answer there although I would give my answer to 1 d.p.

you understand why you do the step with 180 - angle = other possible angle right?
Original post by mqb2766
For b) assuming the numbers are right, what would the obtuse solution be? Why can it be neglected? Tbh. The initial sketch is important. Your 72 angle is far too small.

so the obtuse angle would be 180- 53= 127 degrees. However 127 + 72 > 180 therefore it cannot be that?
Original post by philogrobized
I agree with your answer there although I would give my answer to 1 d.p.

you understand why you do the step with 180 - angle = other possible angle right?

umm i think so, because of the sin graph, so it can be equal to both of the values?
Original post by Rainbowpink1999x
so the obtuse angle would be 180- 53= 127 degrees. However 127 + 72 > 180 therefore it cannot be that?

Correct. Assume there are two solutions corresponding to the two values given by asin(). Then rule out as necessary. Check with a sensible sketch.

Another thing is you can write the rule as
sin(A)/a = sin(B)/b = sin(C)/c
If you're calculating angles, there is less to do at the start (fewer errors). Have a good read of that webpage (or your textbook).
(edited 3 years ago)
Original post by mqb2766
Correct. Assume there are two solutions corresponding to the two values given by asin(). Then rule out as necessary. Check with a sensible sketch.

Another thing is you can write the rule as
sin(A)/a = sin(B)/b = sin(C)/c
If you're calculating angles, there is less to do at the start (fewer errors). Have a good read of that webpage (or your textbook).

appreciate the help, thank you :smile:

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