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Math Help - Radians. how to solve problem.

  1. #1
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    Radians. how to solve problem.

    1) Give the exact value of the following: 4cos(π/4)

    2) Evaluate the following expression when x is π/4. Use the exact value:

    5cos(2x)

    3) For the following expression, find the value of y that corresponds to each value of x, then write your results as ordered pairs (x, y). (Enter your answers from smallest to largest x-value.)


    y=1/4cos(x)

    x=0, π/2, π, 3π/2, 2π




    thxs!
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  2. #2
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    Quote Originally Posted by Nismo View Post
    1) Give the exact value of the following: 4cos(π/4)

    the following expression when x is π/4. Use the exact value:
    \cos\left(\frac{\pi}{4}\right) = \frac{1}{\sqrt{2}}

    You should memorise this value

    therefore 4\cos\left(\frac{\pi}{4}\right) = 4\times \frac{1}{\sqrt{2}}\dots



    Quote Originally Posted by Nismo View Post
    2) Evaluate the following expression when x is π/4. Use the exact value:

    5cos(2x)

     5\cos(2x)

    x=\frac{\pi}{4}

     5\cos(2\frac{\pi}{4})

     5\cos(\frac{\pi}{2})

    You should be able to finish it from here


    Quote Originally Posted by Nismo View Post

    3) For the following expression, find the value of y that corresponds to each value of x, then write your results as ordered pairs (x, y). (Enter your answers from smallest to largest x-value.)


    y=1/4cos(x)

    x=0, π/2, π, 3π/2, 2π


    thxs!
    Insert the values for x one at a time into y, here's the first one.

    y=\frac{1}{4}\cos(x)

    x = 0

    y=\frac{1}{4}\cos(0)

    y=\frac{1}{4}\times 1

    y=\frac{1}{4}
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  3. #3
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    for 1) thats as far as i got then i stopped cause i didnt know how im suspose to cross mutiple the 4 and root2 *edit nvm im so sleep deproved right now i got the answer now....*

    as for 2) its the same thing i got that far and then i got stuck because how do i find a cos of pi/2 is pi/2 is the 90 degree angle?
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  4. #4
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    Quote Originally Posted by Nismo View Post
    is pi/2 is the 90 degree angle?
    Yep

    \pi = 180 \Rightarrow \frac{\pi}{2} = 90
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