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Assume in 3D space there is a point [itex]v=[v_x, v_y, v_z][/tex], and a normal vector associate with it as [tex]n=[n_x, n_y, n_z][/tex]. A line function is defined as [tex]u=w+t\cdot l[/tex] where [tex]w=[w_x, w_y, w_z][/tex] is a point, and [tex]l=[l_x, l_y, l_z][/tex] is the normalized direction of the line. l and n are normalized. Assume there is a function defined as:

[tex]

K = \frac{(u-v)\cdot n}{||u-v||^2}

[/tex]

My question is when point u varies on the line, is the function K varies monotonically???

I've tried to compute [tex]\frac{dK}{dt}[/tex], but I can't really see if it's monotone or not, can some one help me please?

Thanks

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# Monotone Test of the equation

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