alleryIf $G(a, 2, -1)$ is the centroid of the triangle with vertices $P(1, 3, 2),\ Q(3, b, -4),\ R(5, 1, c)$, then $(a, b, c)$ equals:
A$(3, 2, -1)$
B$(3, -2, 1)$
C$(2, 3, -1)$
D$(3, 2, 1)$
Answer & Solution
Correct answer: A. $(3, 2, -1)$
**Centroid formula:** $G = (P + Q + R)/3$.
**Coordinates:** $a = (1+3+5)/3 = 3$, $2 = (3+b+1)/3$
⇒ $b = 2$, $-1 = (2-4+c)/3$ ⇒ $c = -1$.
**So $(a, b, c) = (3, 2, -1)$.**
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