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Why is it when it says Sin(A) he puts theta which is the c angle? and when it says Sin(B) the A angle is put? is there something im missing 

 Oct 21, 2018
 #1
avatar+94321 
+1

Remember  that  cos (120)   =   -cos (60)   =  -1/2

 

So....using the Law of  Cosines

 

BC^2  =  x^2  + (3x)^2  -  2 (x) (3x) (-1/2)

 

BC^2   =  x^2  + 9x^2  + 3x^2

 

BC^2  =  13x^2

 

BC  = x sqrt (13)

 

So.....using the Law of Sines

 

Sin (BCA)  /  x  =  sin (120) / [ x sqrt (13) ]

 

Sin (BCA)  = sqrt (3)  / [ 2sqrt (13) ] =

 

Sin (BCA)  =  sqrt (39) / [ 2 * 13 ]  =   sqrt (39) / 26

 

 

cool cool cool

 Oct 21, 2018

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