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March 28, 2015

Posted by **anon** on Monday, February 21, 2011 at 5:25pm.

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 me. I also have most trouble woth the anti-logarithm.

I am seriously frustrated so you help would be appreciate.

I hope my repost is okay because i wasnt sure if you would go back and check the older post.

Find the area of the following triangles:(use logarithms)

1) c=426, A=45degrees 48' 36",and B=61degrees 2' 13"

- trigonometry (MathMate) -
**MathMate**, Monday, February 21, 2011 at 6:27pmIt is perfectly to repost with a reference to an earlier post.

Here it is:

Given triangle,

A=45-48-36

B=61-02-13

c=426

C=180-00-00 - (45-48-36 + 61-02-13) = 73-09-11

Solve by the sine rule:

a/sin(A)=c/sin(C)

a=c*sin(A)/sin(C)

value logarithm

c 2.6294096

sin(A) 1̅.8555387

c*sin(A) 2.4849483 [ADD]

sin(C) 1̅.9809493

a 2.5039990 [SUBTRACT]

Anti-log 319.1530 (length of c)

Now proceed to calculate area:

Area = (1/2)a*c*sin(B)

value logarithm

(1/2) 1̅.6989700

a 2.5039990

c 2.6294096

sin(B) 1̅.9419744

Area 4.774353 [ADD]

Anti-log 59477.54

Note:

when a number is between 1 and 10, it is normalized, and the logarithm (to the base 10) is between 0 and 1.

Example: log(2) = 0.30103

However, when the number is less than 1, such as 0.5, the decimal is moved one place to the left, and log(5) is recorded (.6989700) with a 1̅ to the left meaning the decimal has been move one to the left.

Conversely, the logarithm of 50 is written simply as 1.6989700, meaning log(5) with one decimal placed to the right.

If you need more details, post (here).

- trigonometry (MathMate) -
**anon**, Monday, February 21, 2011 at 7:25pmokay i was able to get

c*sin(A)= 1.8555387

but i was lost after that. I couldn't reproduce the same answers u have.

value logarithm

c 2.6294096

sin(A) 1̅.8555387

2.4849483 [ADD]

sin(C) 1̅.9809493

a 2.5039990 [SUBTRACT]

Anti-log 319.1530 (length of c)

- trigonometry (MathMate) -
**MathMate**, Monday, February 21, 2011 at 9:51pmAre you able to get the individual logarithms?

For example,

A=45.81°

sin(A)=0.7170323

sin(A)*10=7.170323 (normalize number to between 1 and 10)

Log(sin(A)*10)=0.855387

To move the decimal back one place to the left, we put a (-1) denoted by 1̅ which makes

log(sin(A))=1̅.855387

The we add (instead of multiply) the logarithms

c 2.6294096

sin(A) 1̅.8555387

2.4849483 [ADD]

which is

2.6294096+(-1)+.855387

=2.4849483

Note that the mantissa (the decimal part of the log) is always positive. The characteristics (integer part) are always added separately, and do remember to add the carries, if any.

The subtraction would be calculated similarly.

Please post again if you need more details.

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