# Math

Solve the triangle for x. Side lengths are 9 feet, 8 feet, and 12 feet. x is the angle formed by the sides that are 9 feet and 8 feet long.
a)41.8 degrees
b)89.6 degrees**
c)48.6 degrees
d)90.4 degrees

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1. careful with the signs in the cosine law.
I got cosA = -.0069444.. , which tells me the angle is obtuse, sure enough if
I press 2nd F cos on my calculator, I get 90.3978... , which is d)

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2. law of cosines 12^2 = 8^2++9^2 - 2(8*9)cos A
144 = 64 + 81 - 144 cos A
144 cos A = 1
A = 89.6 deg

cos of 90.4 is the same fraction but negative

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3. Damon is right, I did not follow my own advise and messed up the signs

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4. Whew, I kept going back to check !

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5. Sometimes I just like to do these calculations directly on my
calculator, and that is where I run into difficulties. I should
really write them out first.

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