Trigonometry question

• May 3rd 2010, 06:49 PM
brumby_3
Trigonometry question
Find all sides and angles to the triangle ABC with C a right angle, a=6 and b=4.

I've found c using pythagorus theorm and the answer is 7.21

So I'm trying to find B, and I've done Sin(B)=4/c=4/7.21=0.5547

And so I've pressed the inverse button on my calculator and it keeps giving me the answer 37.439 when the answer should be 33.69... I've already tried an online calculator and it gives me the same answer as I've got on my calculator, and I know the answer is wrong, but how do I get the right answer?
• May 3rd 2010, 08:57 PM
Debsta
Quote:

Originally Posted by brumby_3
Find all sides and angles to the triangle ABC with C a right angle, a=6 and b=4.

I've found c using pythagorus theorm and the answer is 7.21

So I'm trying to find B, and I've done Sin(B)=4/c=4/7.21=0.5547

And so I've pressed the inverse button on my calculator and it keeps giving me the answer 37.439 when the answer should be 33.69... I've already tried an online calculator and it gives me the same answer as I've got on my calculator, and I know the answer is wrong, but how do I get the right answer?

There are 3 angle settings on your calculator. You need to make sure your calculator is set to degrees (at the moment it is set to another measure of angles) hence the answer you are getting is not in degrees.

BTW In these sorts of questions it is best to use primary (given) information so that you don't have compounding rounding errors. It would have been better to use tan(B)=4/6 which avoids using your rounded answer of 7.21 in further calculations.
• May 4th 2010, 12:16 AM
brumby_3
Haha thanks, you're right that was the problem, cheers!