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Let P(2,3,-1) and Q{1,-1,4) be two points in three-dimensional space. [a] Find the distance between P and Q. Answe r: (b) Find an equation for the sphere whose center is P and for which the segment PQ is a radius of the sphere. Answer: ( i2 +[ )2 +[ {c} The vector u has initial point P and terminal point Q. Express vector u in i, j, and k. Answer i+ j+ k