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Math Help - Precal Proof for distance between 2 polar points

  1. #1
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    Post Precal Proof for distance between 2 polar points

    Use the Law of Cosines to prove that the distance between 2 polar points (r1, θ1) and (r2, θ2) is d2=r12+r22-2r1r2cos(θ2-θ1)
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  2. #2
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    Let P_{1}(r_{1},{\theta}_{1}) \;\ and \;\ P_{2}(r_{2}, {\theta}_{2})<br /> <br />
be points in the r{\theta} plane.

    Let a=r_{1}, \;\ b=r_{2}, \;\ c=d(P_{1},P_{2})

    and {\gamma}={\theta}_{2}-{\theta}_{1}

    Sub these into the law of cosines, c^{2}=a^{2}+b^{2}-2abcos{\gamma}, gives the formula.
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