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# Pre-calc

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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
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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
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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