Posted by Anon on Saturday, February 26, 2011 at 3:37am.
I want to start by saying thank you . You have no idea how much u have helped me understand logarithms, even better then the books i have (it poorly explains the subject of trigonometry let alone logarithms and antilog). Your last explanation was very clear and i even understood Law of tangent a little better.
my question was:
Use logarithms and the law of tangents to solve the triangle ABC, given that a=21.46 ft, b=46.28 ft, and C=32°28'30".
give check
You helped me find angle A and B by using logarithms.
A=80 deg 26' 36"
B=67 deg 04' 55"
C=32 deg 28' 30"
a= 21.46
b= 46.28
and I used law of sine to find c.
this is my answer and i would appreciate if you correct me if I'm wrong.
sinA/a = sinC/c
sin 80.443 /21.46 = sin 32.475/c
21.46 (sin 32.475)/(sin 80.443)c
c= 11.68
okay now it says to give check.
okay i honestly don't know how or if the law of sin already covers the check part. I'd like your advice.
and thank you again . I honestly love it when i understand something i thought was so confusingly impossible to understand before.

trigonometry (repost) Mathmate  drwls, Saturday, February 26, 2011 at 6:54am
You can check your value of c by using the Law of Cosines, with the original calyues of a, b and C.
c^2 = a^2 + b^2 2ab cos C
c^2 = 460.32 +2141.84 1986.34*0.8436
c = 30.44
That is not what you came up with. There appears to be something wrong with your initial angles. The law of sines does not agree with your angles A and B. If A > B, than you should have a > b
Perhaps Mathmate can explain the origin of the problem.

trigonometry (repost) Mathmate  MathMate, Saturday, February 26, 2011 at 9:31am
I have looked at the question, and confirm that there was an error in the previous calculations using the law of tangents. Following are results using the sine rule:
Given:
a = 21.46, b = 46.28, C = 322830
The cosine rule gives:
c = sqrt(a^2+b^22*a*b*cos(C))=30.440833
The sine rule gives
A=221432, and
B=1251658
If you draw the triangle, with C=32°, a=21.46 and b=46.28, you will see a skew triangle which shows obviously that B>90°.
So sin(A) has to be interpreted as 180  arcsin() of the acute angle, which gives 1251658 (instead of 544302 straight from the calculator).
I have not completed looking into the source of the error of my previous calculations. It may have to do with the interpretation of the atan() values. I will get back to you when it is done.
I apologize for the inconvenience.

trigonometry (repost) Mathmate  MathMate, Saturday, February 26, 2011 at 10:05am
I just took another look. The formula for the law of tangents should have been tan((A+B)/s)/tan((AB)/2)=(a+b)/(ab).
Previously I have not divided the angles by 2, hence the error.
I will try to make a corrected version and repost in the original post.

trigonometry (repost) Correction  MathMate, Saturday, February 26, 2011 at 6:16pm
The correction to the problem using the tangent rule has been posted at the original post:
http://www.jiskha.com/display.cgi?id=1298609593
Sorry for the inconvenience so caused.
Answer This Question
Related Questions
 trigonometry (MathMate)  MathMate i would really appreciate if you can show me...
 trigonometry  okay so i have this trigonometry problem were i HAVE to use ...
 trigonometry (repost) Mathmate  Use logarithms and the law of tangents to solve...
 trigonometry  Use logarithms and the law of tangents to solve the triangle ABC...
 Trigonometry (Logarthims)  Give checks to the following two questions Use ...
 Trigonometry  Use the properties of logarithms and trigonometric identities to ...
 High School Courses  How often do state colleges which are moderately ...
 Trigonometry  This is more of an opinion question: I'm working on Verifying ...
 Math  Practice Dividing by 9 History : 72 Art: 81 Science: 54 Travel: 63 ...
 english  I have to write a 1000 essay in which I must connect two books ...
More Related Questions