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Math Help - Distance b. Points (Polar Coordinates)

  1. #1
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    Distance b. Points (Polar Coordinates)

    I have the problem: Find the distance between two points: (7,1/2pi) and (1,7/2pi). I got the answer 7. However, someone told me this answer is incorrect--that the correct answer is 11. If 11 is the correct answer, how do I get it?
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  2. #2
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    Hello, Joanie!

    Find the distance between two points: \left(7,\tfrac{\pi}{2}\right)\text{ and }\left(1,\tfrac{7\pi}{2}\right)

    I got the answer 7.
    However, someone told me that the correct answer is 11.

    Sorry, you're both wrong . . . Did you make a sketch?
    Code:
                  |
                  o (7, π/2)
                  |
                  |
                  |
                  |
                  |
        - - - - - + - - - - - -
                  |
                  o (1, 7π/2)
                  |
                  |

    Their distance is 8, isn't it?

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  3. #3
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    Smile Reply to Polar Coordinates Help

    I am using the formula:

    Point 1, Point 2 = Square root of r1^2+r2^2-(2)(r1)(r2)cos(theta2 - theta1)

    square root of (7^2+1^2-2(7)(1)cos(1/2pi-7/2pi)

    sq. rt. of 50-14cos(-540)
    sq.rt of 50-14(.9380)
    sq. rt. 50 + 13.132
    sq. rt. 63.132
    = 7

    My possible answers are 11, 7, 8, 10

    How can I get the answer 8 using this formula?
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  4. #4
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    Distance between two points in polar coordinates

    Hello Joanie
    Quote Originally Posted by Joanie View Post
    I am using the formula:

    Point 1, Point 2 = Square root of r1^2+r2^2-(2)(r1)(r2)cos(theta2 - theta1)

    square root of (7^2+1^2-2(7)(1)cos(1/2pi-7/2pi)

    sq. rt. of 50-14cos(-540)
    sq.rt of 50-14(.9380)
    sq. rt. 50 + 13.132
    sq. rt. 63.132
    = 7

    My possible answers are 11, 7, 8, 10

    How can I get the answer 8 using this formula?
    Soroban has showed you the simplest way, but if you want to know where you've gone wrong, look at the bit in red. You'd got your calculator set in radians, not degrees!

    Grandad
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