Question

Let (3, 4, -1) and (-1, 2, 3) be the end points of a diameter of a sphere.

Then, the radius of the sphere is equal to

• A. 2
• B. 3
• C. 6
• D. 7

Answer 1

The correct option is B

3

Suppose d is the diameter of the sphere. Then

$d^2=(-1-3{)}^2+(2-4{)}^2+(3+1{)}^2$

$\Rightarrow d^2=(-4{)}^2+(-2{)}^2+(4{)}^2$

$\Rightarrow d^2=16+4+16$

$\Rightarrow d^2=36$

$\Rightarrow$ d = 6

Hence, radius of the sphere is 3 units.