Please check my work...

Sep 2009
37
1
Hi,

136.6025404sin30 = 68.30127019 according to my calculator. However, my teacher has marked my work and says it equals 68.20 rounded to 2 decimal places.

Can someone please check and see what they get? I can't see why our answers differ.

Thanks
Splint
 

mr fantastic

MHF Hall of Fame
Dec 2007
16,948
6,768
Zeitgeist
Hi,

136.6025404sin30 = 68.30127019 according to my calculator. Mr F says: Correct.

However, my teacher has marked my work and says it equals 68.20 rounded to 2 decimal places.

Can someone please check and see what they get? I can't see why our answers differ.

Thanks
Splint
Where has 136.6025404sin30 come from? Perhaps the error, if any, is in this expression rather than in its value ....
 
Sep 2009
37
1
Where has 136.6025404sin30 come from?
Thanks for your reply Mr Fantastic, 136.6025404 is the length of the hypotenuse and 30 is the angle in degrees which, when calculated as shown above produces the length of the opposite side.

Have a nice day...
 
Feb 2010
1,036
386
Dirty South
Hi,

136.6025404sin30 = 68.30127019 according to my calculator. However, my teacher has marked my work and says it equals 68.20 rounded to 2 decimal places.

Can someone please check and see what they get? I can't see why our answers differ.

Thanks
Splint
It should be 68.30 because sin30 = 1/2, and 136.6025404 * 1/2 = 68.3012702

It would be easier to spot your problem if you posted the entire question!
 
Sep 2009
37
1
It would be easier to spot your problem if you posted the entire question!
The question shows a right angle triangle where the opposite side is unknown. There is a line drawn from one corner of the triangle which makes another triangle within the right angle triangle, the hypotenuse is a common side of both triangles, part of the adjacent side is common to both triangles and the opposite side is exclusive to the right angle triangle. The sine rule is used to find the length of the hypotenuse, which in turn is used to find the length of the opposite side. I hope that's not too confusing, a picture would be much easier.


h/sin(135) = 50/sin(15)

hsin(15) = 50sin(135)

h = 50sin(135)/sin(15)

h = 136.6025404 (hypotenuse)

136.6025404sin(30) = 68.30127019 (opposite side length)

Having said all that I suspect my teacher has simply made a mistake. I'll send her an email and ask her to check it again, hopefully she'll have time.