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Extreme values on a helix Suppose that the partial derivatives of a function $$f ( x , y , z )$$ at points on the helix $$x = \cos t , y = \sin t$$ , $$z = t$$ are $$f _ { x } = \cos t , f _ { y } = \sin t , f _ { z } = t ^ { 2 } + t - 2$$ .
$$( \cos 1 , \sin 1,1 ) \text { and } ( \cos ( - 2 ) , \sin ( - 2 ) , - 2 )$$