The surface given by the parametric equations
(1)
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(2)
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(3)
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For , the coefficients of the first fundamental form are
(4)
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(5)
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(6)
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and of the second fundamental form are
(7)
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(8)
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(9)
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The Gaussian and mean curvatures are given by
(10)
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(11)
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and the principal curvatures are
(12)
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(13)
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