alleryThe point dividing the line segment joining $A(2, -6, 8)$ and $B(-1, 3, -4)$ internally in ratio $1:3$ has coordinates:
A$(5/4, -15/4, 5)$
B$(-7/2, 21/2, -14)$
C$(1/4, -1/4, 2)$
D$(7/2, -21/2, 14)$
Answer & Solution
Correct answer: A. $(5/4, -15/4, 5)$
$\vec r = (1\cdot \vec b + 3\cdot \vec a)/(1+3) = (1(-\hat i+3\hat j-4\hat k) + 3(2\hat i-6\hat j+8\hat k))/4 = (5\hat i -15\hat j +20\hat k)/4$
giving $(5/4, -15/4, 5)$.
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