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

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()

2. Google arcsin((sin(62)/7)*8) and you'll get its value: -1.00615005

3. Originally Posted by kuku9017
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()

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.)

4. Originally Posted by kuku9017
[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.

sin(62°)/7=sin(B)/8

(sin(62°)/7)*8=sin(B)

sin^-1((sin(62°)/7)*8)=B