SECTION 2.4COSINE LAW
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I) WHAT IS THE COSINE LAW
The Cosine Law is for solving triangles that are NOT R.T.
You could only use the Cosine Law when you have:
2 sides and the angle in between
All 3 sides and need to find the angles
Finding side “a” or angle A
Finding side “b” or angle B
Finding side “c” or angle C
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EX: FIND THE VALUE OF THE MISSING SIDE “X”
Indicate which side you want to find
Plug the values into your formula
Indicate which side you want to find
Plug the values into your formula
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II) FINDING ANGLES WITH THE COSINE LAW
When finding angles, isolate the cosine function first
Then use inverse cosine to find the angle
The side opposite of the angle must be on the left of theequation
Indicate which side you want to find
Plug the values into your formula
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Practice: Find the missing angle
Indicate which side you want to find
Plug the values into your formula
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Practice: FIND THE AREA OF THE TRIANGLE
Find one of the angles
Use the angle to find the height ofthe triangle
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HW
Assignment 2.4