Mathbook problem - Geometry

Math and Physics Programming

Started by Basse85 March 12, 2012 08:34 PM

6 comments, last by Basse85 12 years, 1 month ago

308

Author

March 12, 2012 08:34 PM

I got this problem and im not going to meet the teacher untill next monday and i want to progress further so maby you can help me?
The question is:

What are the angels of the triangle ABC if
A = 2B
B < 45 degres
SinC = 0.5

Thanks in advance

Ripiz

539

March 13, 2012 11:42 AM

sin C = 0.5, meaning C is 30 degrees, therefore we have 150 degrees left for the other 2 angles.

A = 2B
A + B = 150
Wolfram solves it with result of A = 100, B = 50 (the only solution)
However you said B < 45, meaning it cannot be solved or you wrote/read something incorrectly.

alvaro

21,604

March 13, 2012 12:25 PM

sin C = 0.5 means either C is 30 degrees, or C is 150 degrees. Ripiz just explained why it can't be 30 degrees, therefore it's 150 degrees, A is 20 degrees and B is 10 degrees.

alvaro

21,604

March 13, 2012 12:33 PM

By the way, Wolfram alpha can do the whole thing (in radians).

Basse85

308

Author

March 13, 2012 10:00 PM

I also got C = 30, thats what the calc says. How do you know it can also be 150?

Thanks

alvaro

21,604

March 13, 2012 10:22 PM

I also got C = 30, thats what the calc says. How do you know it can also be 150?

I don't know... A decent high school education?

What do you know about the sine function? The way I think about it, it's the height of a point in the trigonometric circle. It should be fairly obvious then that sin(x) = sin(180 degrees - x).