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Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
Non-Right Angled Trig - The Law of Sines
What do we know how to find with non-right angled triangles?
Using the area of this triangle...
Proof for the Law of Sines
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
*We can ONLY use this when we have an angle and it's opposite side!
The Law of Sines
*this is in your booklet!
This can be used for right triangles but typically is not!
17.5
50
18.4
12
126
112
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
13.3 km
What happens when we try to use the sine rule?
Doesn't work, we are missing the side opposite the given angle!
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
Therefore we need another rule...The Cosine Rule!
There are TWO situations where you use the cosine rule.
1. SAS - two sides and the included angle
2. SSS - all three sides
Find the missing side first!
Then use the Sine Rule.
Find ANY angle first!
Then use the Sine Rule
We can derive the formula using Pythagorean Theorem.(watch the video on the website!)
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
From a triangle using standard labeling,
the cosine rule is:
What important relationship do
you notice?
10.1
33.9
77.1
84.4
75.0
20.6
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
Solve the following triangles - EXTRA PRACTICE:
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
Law of Sines and Cosines - w/ Answers
IBSL Year 1
February 11, 2016
Homework
Chapter 11.4
11G: 1-4
11I: 1-6