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M2201 section 3.3.notebook
13.3 Page 1
3.3 Proving and Applying the Cosine Law
The law of sines cannot always be used to determine missing angles or side lengths.
For example, consider the following triangles:
M2201 section 3.3.notebook
2Nov 1010:30 AM
Since we can draw an altitude from any of the vertices the law of cosines can be written as:
(missing side)2 = (side 1)2 + (side 2)2 2(side 1)(side 2) (cos contained angle)
Example : Find the length of p in the diagram below:
Use the Cosine law to find a missing length
M2201 section 3.3.notebook
3Sep 111:51 PM
Example : Find the length of AC in the diagram below:
Example : Find the length of AC in the diagram below:
M2201 section 3.3.notebook
4Nov 1011:18 AM
Use the Law of Cosines to find a missing angle.
It is helpful to rearrange the formula as follows:
α
l 2 = m2 + n2 2mn cos L
2mn cos L= m2 + n2 l 2
cos L= m2 + n2 l 2 2mn 2mn
cos L = m2 + n2 l 2 2mn
Example: Determine the measure of
M2201 section 3.3.notebook
5Nov 102:40 PM
Example: In ΔABC a = 51 cm,
M2201 section 3.3.notebook
63.3 Page 10
Page 151 153 # 4 10, 12, 13
Attachments
PM113s3.gsp
3s3e1 final.mp4
3s3e2 final.mp4
SMART Notebook
SMART Notebook
SMART Notebook
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