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How do I solve a triangle with side a=8 and b=10 and c=12 using law of sines and cosines?????? any help appreciated and all steps shown out would be super great thanks! :)

 Apr 16, 2015

Best Answer 

 #1
avatar+130516 
+5

We can use the Law of Cosines to find one angle  and then the Law of Sines to find the next one. Choosing any one side, we have

12^2  = 10^2 + 8^2 -2(10)(8)cosC  simplify

144 = 100 + 64 - 160cosC   which implies that .....

[144 - 100 - 64] / [ -160] = cosC

1/8  = cosC

Using the inverse cosine, we have

cos-1 (1/8)  = C = about 82.8°

And using the Law of Sines, we can find B, thusly:

sin B / 10 = sin 82.8 / 12

sinB = 10sin(82.8) / 12

sin-1  [10sin(82.8) / 12]  = B = about 55.77°

And angle A can be found by subtracting the sum of B and C from 180

 

  

 Apr 16, 2015
 #1
avatar+130516 
+5
Best Answer

We can use the Law of Cosines to find one angle  and then the Law of Sines to find the next one. Choosing any one side, we have

12^2  = 10^2 + 8^2 -2(10)(8)cosC  simplify

144 = 100 + 64 - 160cosC   which implies that .....

[144 - 100 - 64] / [ -160] = cosC

1/8  = cosC

Using the inverse cosine, we have

cos-1 (1/8)  = C = about 82.8°

And using the Law of Sines, we can find B, thusly:

sin B / 10 = sin 82.8 / 12

sinB = 10sin(82.8) / 12

sin-1  [10sin(82.8) / 12]  = B = about 55.77°

And angle A can be found by subtracting the sum of B and C from 180

 

  

CPhill Apr 16, 2015

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