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In triangle ABC, we have AB = 5, BC = 8, and AC = 9, as shown below

 

 

Calculate cos A, cos B, cos C.

 Feb 7, 2022
 #1
avatar+2444 
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cos = \(\text{adjacent}\over\text{hypotenuse}\)

 

The hypotenuse is always the longest side, and adjacent is the one side that is next to the relative position of the vertice that is being "cos'ed". For example:  \(\color{brown}\boxed{{\cos A} = {5\over 9}}\). You can solve the rest from here. Good Luck!

 Feb 8, 2022
 #2
avatar+36434 
+1

BuliderBoi....  

    That definition only works in RIGHT TRIANGLES

 

to solve this problem you will need to use the Law of Cosines

   c^2 = a^2 + b^2 - 2ab cos (angle c)

 

For cos A

 

  8^2  = 9^2 + 5^2 - 2(9)(5) cos A      then solve for cos A        The others are similar .....

 Feb 8, 2022

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