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Math Help - Polar Coordinates

  1. #1
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    Polar Coordinates

    Find the polar coordinates of this point with the given rectangular coordinates. Use 0 < or = theta < 2pi and r > or + to 0.

    (-2, -5)

    I understand how to get r but how do i get theta expressed in pi?
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  2. #2
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    Quote Originally Posted by acherucheril View Post
    Find the polar coordinates of this point with the given rectangular coordinates. Use 0 < or = theta < 2pi and r > or + to 0.

    (-2, -5)

    I understand how to get r but how do i get theta expressed in pi?
    Your answer won't be "expressed in terms of pi", but it needs to be in radians.

    Draw a diagram. Construct a right angled triangle in the third quadrant (where (-2, -5) is.
    Use trigonometry (tan^-1) to find the acute angle below the neg x-axis ( this must be in radians). Add this angle to pi (to get the total angle anticlockwise from the pos x-axis). Then you'll have theta.
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    Quote Originally Posted by Debsta View Post
    Your answer won't be "expressed in terms of pi", but it needs to be in radians.

    Draw a diagram. Construct a right angled triangle in the third quadrant (where (-2, -5) is.
    Use trigonometry (tan^-1) to find the acute angle below the neg x-axis ( this must be in radians). Add this angle to pi (to get the total angle anticlockwise from the pos x-axis). Then you'll have theta.
    Ok so i do [ tan^-1(-5/-2) + pi ] ?
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  4. #4
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    Quote Originally Posted by acherucheril View Post
    Ok so i do [ tan^-1(-5/-2) + pi ] ?
    Yes, although I'd leave off the neg signs on the 5 and the 2. (It won't make a difference in this case). Find the acute angle then add pi.
    Note: If the point was (-2, +5), you'd find the same angle (this time in the second quadrant) and subtract it from pi.
    A diagram makes everything clear.
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  5. #5
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    Quote Originally Posted by Debsta View Post
    Yes, although I'd leave off the neg signs on the 5 and the 2. (It won't make a difference in this case). Find the acute angle then add pi.
    Note: If the point was (-2, +5), you'd find the same angle (this time in the second quadrant) and subtract it from pi.
    A diagram makes everything clear.
    how do you change 248.1985905 into radians?
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  6. #6
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    Quote Originally Posted by acherucheril View Post
    how do you change 248.1985905 into radians?
    Mutiply by pi/180.
    Better still switch your calculator to radian mode in the first place
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  7. #7
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    so if i changed it to radian mode, it equals 1.37pi. How do i turn that into something thats on the unit circle?
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  8. #8
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    nvm again.
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