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I was given a triangle:

side opposite of angle A: unknown, referred to as L

side adjacent of angle A: 11'

hypotenuse: 14'

I have to find the cosine of angle A, the degrees, and the length of "L", opposite angle A, in feet.

L is equal to 8.6602, which in feet is 8'-7 7/16. I did the math, and got angle A= 38 degrees

(my instructor wants length in feet-inches-fraction, I'm in pipefitters school. He also doesn't want minutes or seconds for the angles)

However, when I did the cosine function, I ended up with .999905 We are supposed to round decimals to the fourth place. However, that leaves me with

.9999

which should round up to

1

But...what I'm wondering is can I even have a whole number for a cosine, or should I leave it at .9999?

If .9999 is the mathematically correct answer, I need to know why, in order to defend it in class. If 1 is the correct answer, then I'd just like to know why. However, I asked Google and haven't been able to get an answer that I understand.

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    Since I up-voted this question and it's total is $0$, someone must have down-voted it, showing again the inefficacy of that as a communications medium, since there's no way to know why.2012-03-12

1 Answers 1

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You found the cosine of $11/14$ degrees. But you needed the arccosine (not the cosine) of $11/14$. Just $11/14$, not $11/14$ degrees. The calculator in front of me gives $ \cos^{-1} \frac{11}{14} \approx 38.2^\circ. $

The cosine of $11/14$ degrees is about $0.9999059$, but that's not what you need here.

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    And $11/14$ degrees is equal to about 0.0137, which is indeed very close to zero.2012-03-11