An 'undefined' answer with sine rule [non-right angled triangles]

kuku9017

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Jan 30, 2018
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Hi. So I just created a question for myself regarding the sine rule for non-right angled triangles and something odd came up. I just needed to do one last thing to get the answer and when I did it, it ended up being 'undefined'. Here is the working out:

Angle C=62 [degrees]
Side c= 7cm
Side b = 8cm

Find angle B:

sin(A)/a=sin(B)/b=sin(C)/c

sin(62)/7=sin(B)/8
(sin(62)/7)*8=sin(B)
sin^-1((sin(62)/7)*8)=B

And when I do that step it says undefined. I tried doing sin(62)/7 first, then doing that *8, then putting all that within the brackets of sin^-1()

Nothing has worked so far... Please help!!!
 
Hi. So I just created a question for myself regarding the sine rule for non-right angled triangles and something odd came up. I just needed to do one last thing to get the answer and when I did it, it ended up being 'undefined'. Here is the working out:

Angle C=62 [degrees]
Side c= 7cm
Side b = 8cm

Find angle B:

sin(A)/a=sin(B)/b=sin(C)/c

sin(62)/7=sin(B)/8
(sin(62)/7)*8=sin(B)
sin^-1((sin(62)/7)*8)=B

And when I do that step it says undefined. I tried doing sin(62)/7 first, then doing that *8, then putting all that within the brackets of sin^-1()

Nothing has worked so far... Please help!!!

You've found that sin(B)=1.00908296. There is no angle with this sine, so you've shown that there is no solution -- no such triangle exists.

Try drawing the triangle, and see what happens!

(By the way, Google takes 62 to be radians, which is why it doesn't show an error.)
 
[degrees]
I missed that.

I think it's a good idea to use a degree symbol, when writing angle measurements in degrees, but I understand a lot of instructors don't do that. :cool:

sin(62°)/7=sin(B)/8

(sin(62°)/7)*8=sin(B)

sin^-1((sin(62°)/7)*8)=B
 
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