Question

If $(1,1,a)$ is the centroid of the triangle formed by the points $(1,2,-3)$ , $(b,0,1)$ and $(-1,1,-4)$ then $a-b$ $=$

• A. $-5$
• B. $-7$
• C. $5$
• D. $1$

Answer 1

Answer: (A)

$-5$

The coordinates of the vertices of the triangle are given by $(1,2,-3),(b,0,1),(-1,1,-4)$

Accordingly the coordinates of the centroid of this triangle will be given by

($\frac{b}{3},1,-2$)

Hence, $\frac{b}{3}$ $=1$ Or, $b=3$

and $a=-2$

So $a-b=-5$