: . (x - a)/ l = (y - b) /m = (z - c) / n = t
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(x-a)/l = t
x = lt + a < = > x = 0
: . a = 0 < = > t = 0
(y-b)/m = t
y = mt + b <=> y = 5+5t
: . m = 5
b = 5
(z-c)/n = t
z = nt + c <=> z = 1 + t
: . n = 1
c = 1
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: . P2 = (0,5,1) & P1=(5,5,2)
: . D = √[(0-5)2 + (5-5)2 + ( 1-2)2 ]
= √ [(-5)2 + (-1)2 ]
= √26
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Goodluck!