Posted by **Anon** on Monday, February 28, 2011 at 8:30pm.

This is an outline that i have to use to find the solution of the question. It involves logarithms and half-angle formulas.I have worked though it but got stuck on some parts. I'd like if you look over my work.

solve the triangle for which given parts are

a=27 ,b=21 ,c=24

Now i used the cosine law and got the answers

A=73 deg 23' 55"

B=48 deg 11' 23"

C=58 deg 24' 43"

...................

okay now for this outline;

a=27

b=21

c=25

----

2s=73

s=36.5

s-a=9.5

s-b=15

s-c=11.5

log(s-a)= .97772

log(s-b)=1.19033

log(s-c)=1.06070

--------

=3.22875

log s =1.56229

--------

2)1.66646

--------

log r =0.83323

now this part I'm having trouble with.

log r = 0.83323

log(s-a) = 0.97772

--------

log tan A/2 = 9.85551 - 10

A = ? << can you help me convert.

log r = 0.83323

log (s-b) = 1.19033

--------

log tan B/2 = 9.64290 - 10

B = ? same here my brain freezes

log r = 0.83323

log (s-c) = 1.06070

--------

log tan C/2 = 9.77253 - 10

C = ?

A+B+C= 180 deg 0' 2"

do they match?

- trigonometry -
**Reiny**, Monday, February 28, 2011 at 8:47pm
I noticed an error in your outline

log(s-b) = log 15 = 1.17609 you have 1.19033

Your outline suggests to me Heron's formula for finding the area of a triangle.

I didn't see anything about area of triangle in your question

then I see log r =0.83323

where does r come from ?

To do a calculation like

log tan A/2 = 9.85551 - 10

A = ?

I had already shown you how to do that in one of your previous posts

http://www.jiskha.com/display.cgi?id=1298862691

- trigonometry -
**Anon**, Tuesday, March 1, 2011 at 3:08am
that was a typo its 15.5 which makes the log entry correct.

=3.22875

log s =1.56229 subtract.

--------

2)1.66646 <<.. then divide by 2 =

--------

log r =0.83323

the reason why i posted the out line was because they did not match. and i didn't understand how you got the inverse tangent .

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