trigonometry (repost) Mathmate

posted by .

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 -

    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 -

    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:

    a = 21.46, b = 46.28, C = 32-28-30
    The cosine rule gives:
    c = sqrt(a^2+b^2-2*a*b*cos(C))=30.440833
    The sine rule gives
    A=22-14-32, and

    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 125-16-58 (instead of 54-43-02 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 -

    I just took another look. The formula for the law of tangents should have been tan((A+B)/s)/tan((A-B)/2)=(a+b)/(a-b).
    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 -

    The correction to the problem using the tangent rule has been posted at the original post:
    Sorry for the inconvenience so caused.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Trigonometry

    This is more of an opinion question: I'm working on Verifying Identities but I always have trouble knowing where to start. Once my teacher points it out i'm like "oh, duh" but on my own I have not the slightest idea on how to begin …
  2. High School Courses

    How often do state colleges which are moderately competitive require trigonometry?
  3. english

    I have to write a 1000 essay in which I must connect two books together. Yann Martel's "Life of Pi" and Tim O'Briens "The Things They Carried" The thing is, I have no idea where to even start. Any ideas for premises, thesis statement …
  4. trigonometry

    okay so i have this trigonometry problem were i HAVE to use logarithms. Now this is my work but can u help me solve it using logarithms. Find the area of the following triangles:(use logarithms) 1) c=426, A=45degrees 48' 36",and B=61degrees …
  5. trigonometry (MathMate)

    MathMate i would really appreciate if you can show me where the logarithms can be used.I know they are unnecessary and I already found the answer without them but i still have to show my work using logarithms and they just confuse …
  6. Trigonometry (Logarthims)

    Give checks to the following two questions 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" without logarithms i can do this problem easily and i have. but when i …
  7. trigonometry

    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" Also Give checks. I know the use of logarithms is unnecessary but i have to show my solution by using logarithms …
  8. trigonometry (repost) Mathmate

    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" Using the previous values, a=21.46 b=46.28 C=32-28-30=32.475 We have A+B=180-32.475=147.525 a+b=67.74 a-b=-24.82 …
  9. Trigonometry

    Use the properties of logarithms and trigonometric identities to verify the identity. ln|cot x| = ln|cos x| - ln|sin x| I have no idea where to begin with this one... your help is appreciated!
  10. Math

    Practice Dividing by 9 History : 72 Art: 81 Science: 54 Travel: 63 Fiction: 90 Biography: 45 Poetry: 27 Cooking: 36 1/Raul might put an equal number of each kind of book on 9 shelves. How many types of books will have an even number …

More Similar Questions