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A point R divides the line joining P (position vector a) and Q (position vector b) INTERNALLY in the ratio m:n. The position vector of R is:
A$(a + b)/2$ (midpoint)
B$(a × b)/(m + n)$ (cross product)
C$(mb + na)/(m + n)$ (internal division)
D$(mb − na)/(m − n)$ (external division)
Answer & Solution
Correct answer: C. $(mb + na)/(m + n)$ (internal division)
Internal division formula: r = (mb + na)/(m + n). External division: r = (mb − na)/(m − n). Midpoint is the special case m = n = 1.
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