Solution Let A, B, C be the three points in the plane D is the foot of the perpendicular
drawn from a point P to the plane PD is the required distance to be determined, which
is the projection of AP
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 on AB
AC
×
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not to be republished
 MATHEMATI CS
496
Hence, PD = the dot product of AP
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  with the unit vector along AB
AC
×
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