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Show that the curve $$\ell$$ given by $$r = a \cos t \sin t i + a \sin ^ { 2 } t j + a \cos t k , ( 0 \leq t \leq \frac { \pi } { 2 } )$$
$$\frac { a ^ { 2 } } { 2 } ( \sqrt { 2 } + \ln ( 1 + \sqrt { 2 } ) )$$