dessyk
need help im going to draw a triangle and im doing the law of sines so if anyone can help please do cuz im confused.. please click this to helpp
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dessyk
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|dw:1335063015673:dw|
GT
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Do you need to find a?
dessyk
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so let me explain im trying to find a okay c=96.3, b=145.67 , B=39.5degrees, C=74.2degrees,
dessyk
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law of sines is a/sinA=b/sinB
GT
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Sine rule says:
SinA/a = SinB/b = SinC/c
dessyk
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okay i understand that
waitt why is it sina/a instead of a/sin a
GT
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SinA/a = Sin(39.5)/145.67
SinA = a*something
GT
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Because they mean the same thing. A/B = C/D => B/A = D/C
dessyk
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waitt does it even matter
dessyk
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okay im not understanding
GT
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You can find angle A by simply subtracting angles B and C from 180.
dessyk
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okay i understand which would be 66.8
GT
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Then, use this:
SinA/a = Sin(39.5)/145.67
SinA = a*something
SinA/something = a
To find a.
GT
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SinA/a = SinB/b = SinC/c
IS SAME AS
a/SinA = b/SinB = c/SinC
dessyk
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but then a would be .00436
GT
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I am getting 210.5
GT
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That "something" in my expression is 0.00436. Divide Sin66.8 by that "something" value. Then, you get the value of a.
dessyk
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really then let me try again...... im still not getting that are you multiplying or dividing
GT
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SinA/a = Sin(39.5)/145.67
SinA = a*0.00436
a = SinA/0.00436
a = Sin66.8/0.00436
a = 210.5
dessyk
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im not getting it first you divided than you did something else im so confused
dessyk
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ok
dessyk
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i also had another question
GT
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Post it separately.
dessyk
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i dont understand
imagreencat
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Which part don't you understand? :) I can help you.
dessyk
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okay, so instead of 66.8 its 66.3
dessyk
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im so fustrated im confusedd
GT
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Punch it into the calculator and you get slightly different number from 210.5
GT
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SinA/a = Sin(39.5)/145.67
SinA = a*0.00436
a = SinA/0.00436
a = Sin66.3/0.00436
a = 210
dessyk
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i neeed helpppp
dessyk
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i got -47.99
imagreencat
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Check your calculator first. I'm guessing you're getting different answers because your calculator is not in degree mode. That's why it's treating your angles differently.
dessyk
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wait no i got -110.05
GT
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How in the world can a length of a side of a triangle be negative? Can you show the arithmetic you used to get that number?
dessyk
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yeppp m ycalculator wasnt in degree mode so let me try again
dessyk
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yayy i got 209.69
GT
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Good....close enough to 210. :)
dessyk
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next problem
b=58.2
c=68.3
C=51.3 degrees
were gunna find a
GT
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At this point, it is simply plugging in values into that sine rule ratios and cranking out numbers in a calculator. There is not much help you need.
dessyk
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yeaa but i want to do it my self then have someone do it so i can nn check my answer to make sure its correct
dessyk
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i got 7105. 88
dessyk
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is my answer correct thats all im asking
GT
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It can't be that big.
GT
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Angles are almost close to each other. So, side lengths have to be close to each other too.
dessyk
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well i must be doing something wrong but sin68.3/51.3=.018111746
dessyk
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128.7/.018111746=7105.88
GT
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b=58.2 c=68.3 C=51.3 degrees
SinB/b = SinC/c => SinB = 58.2 * Sin(51.3)/68.3 => SinB = 0.665
B = 41.68
dessyk
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becuase i couldnt find A or B so i figured they were the same
by suntracting 180-51.3
dessyk
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ohhh ok so u must follow the formula
GT
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Now that you know B, you find A by doing 180 - 51.3 - 41.68 = 87
dessyk
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noww i get it
GT
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SinA/a = SinC/c
=> a = c * SinA/SinC
=> a = 68.3 * Sin(87)/Sin(51.3)
=> a = 87.4
dessyk
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ok
wombat
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@dessyk
The following variations of Law of Sines are the same:
\[\frac{a}{\sin(A)} = \frac{b}{\sin(B)}=\frac{c}{\sin(C)}\]
and
\[\frac{\sin(A)}{a}=\frac{\sin(B)}{b}=\frac{\sin(C)}{c}\]
GT
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He got that. :)
wombat
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ok :)
dessyk
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hello
GT
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yeah
dessyk
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i have another question but hoew did you get 41. sometrhing but i got 45.42
GT
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You mean for B = 41? I did the inverse sine function on the value 0.665.
dessyk
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yes, ohh reallyy you see im confused now i thought u just i thought u just took .6650*68.3=45.42
GT
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Sin(B) = 0.665
=> B = inverse sine (0.665). On the calculator, you have to first press 0.665. Then, inv button, then the sin button.
GT
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That gives you angle B.
dessyk
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i didnt get that
jatinbansalhot
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dessyk.. nice drawing.. :) :)
dessyk
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thank you i guesss lol can yoiu help me!!
jatinbansalhot
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what is the question
dessyk
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its up above next problem
b=58.2
c=68.3
C=51.3 degrees
were gunna find a
dessyk
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law of sines
jatinbansalhot
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i didn't see above but u can find it very easily..
the formula is
sin a / a = sin b / b = sin c / c
or
a /sin a = b / sin b = c / sin c
use any of them what caters ur problem
dessyk
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okay but when i tried i started to get fustrated because i wasnt getting the righ tanswer
jatinbansalhot
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did my answer help u even a bit or not ?
dessyk
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a little bit its just that i need help going through the process
petewe
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|dw:1335070736451:dw|
petewe
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|dw:1335070848159:dw|
petewe
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get it?