Hello
I'm practicing for my A-level exams, and have this problem: ∆PQR in which p=3km, q=23km, R=10°
I use the Cosine Rule to solve for r, which is 20.05km. So far so good, and the book confirms I am correct.
Now to find the remaining angles. So I use the Sine Rule: a / Sin(A) = b / Sin(B)
I use the Sine Rule to solve for P. I get 1.49°. And the book confirms I am correct. All good.
Finally, I use the Sine Rule to solve for Q:20.0524 / Sin(10) = 23 / Sin(Q)I get... 11.49° !? Obviously wrong, because the total degrees of a triangle always add up to 180°. But I've checked and re-checked, and I'm solving it with the exact same steps, and Rule, with which I solved for P. I even tested it on a math solving website - I get the same result(!):
http://www.cymath.com/answer.php?q=solve%20(20.0524)%2F(sin(10))%3D(23)%2F(sin(Q))
What is going wrong??My calculator is set to degrees, and I re-checked that. Does Sin only work upto a certain number of degrees (no mention of this in the book).
Any help would be very appreciated.