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Math Help - solving cos.

  1. #1
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    solving cos.

    Hi! If anyone could please explain this, I would really appreciate it.
    Thanks in advance!

    I'm doing my math hw and trying to use the calculator as little as possible.
    one of the problems is verifying the x-value.
    the step I am currently on looks like this:

    4cos^2 (45 degrees) -2 =0

    my question is. Could anyone possibly explain how to find 4cos^2 (45) by hand (not using a calculator)????? When I put it into the calculator it says te answer is 2. But I want to know how to find that by hand...is it possible???
    do you square the 45 first and then multiply by 4 and find the cos of that?????

    thanks again!!!
    and please let me know if my question does not make sense :/
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by overduex View Post
    Hi! If anyone could please explain this, I would really appreciate it.
    Thanks in advance!

    I'm doing my math hw and trying to use the calculator as little as possible.
    one of the problems is verifying the x-value.
    the step I am currently on looks like this:

    4cos^2 (45 degrees) -2 =0

    my question is. Could anyone possibly explain how to find 4cos^2 (45) by hand (not using a calculator)????? When I put it into the calculator it says te answer is 2. But I want to know how to find that by hand...is it possible???
    do you square the 45 first and then multiply by 4 and find the cos of that?????

    thanks again!!!
    and please let me know if my question does not make sense :/
    4cos^2(45^o) = 4 ( cos(45^o) )^2 = 4 \left ( \frac{\sqrt{2}}{2} \right ) ^2 = 4 \frac{2}{4} = 2

    -Dan
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