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Multiply a trigonometry function

  1. May 3, 2012 #1
    I have a question I have learn a bit about trigonometry and I came across this formula

    angle = 38
    length = 120

    length * sin( angle )

    now I have look around for the understanding about this formula and tested the formula my self


    120 * sin( 38 )


    sin( 38 )

    And as you can see they both calculate the same number, Why is this and what would be the point in using this formula.
  2. jcsd
  3. May 3, 2012 #2


    User Avatar
    Science Advisor

    Hey Pin Head and welcome to the forums.

    Your figures are not correct. Using a calculator I get the following:

    sin(38) = 0.2963686
    120 * sin(38) = 35.56423

    In terms of what this means, it is a projection of some vector with length given by length projected on to the x-axis. If you replace sin with cos you get the projection onto the y-axis.
  4. May 3, 2012 #3
    You are correct I don't no why my calculator is giving me
    but when I tested the same equation in java programming,java gives me the answer you gave

    sin(38) = 0.2963686
    120 * sin(38) = 35.56423

    So what would this formula be good for?
  5. May 3, 2012 #4


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    Science Advisor

    Like I said above, it's useful for taking a vector and finding the x and y components of the vector.

    Vectors are used in many things including physics. For example we can represent a vector to represent a force like gravity, or even a force on something like an electron.

    Lets say we have a vector (a,b) which is a two-dimension vector. We calculate our length to be length = SQRT(a^2 + b^2) where SQRT is the square root function. We also calculate our angle to be angle = tan(b/a).

    Now given an angle and a length we can find our x and y components. We do this by using the relationship x = length x sin(angle) and y = length x cos(angle).

    This is just one reason and there are many others. But if you think about how all the scientists, engineers, and others work with systems that have vectors, then you will start to see how this is useful.
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