What is the value of r if the distance between the point (4,2) and (1,r) is 3 units?
A
1
B
2
C
3
D
4
Verified Correct Answer: B.
Step-by-Step Mathematical Solution
A(4,2) and B(1,r), AB = 3 units
3 = \sqrt (x2- x1)2 + (y2-y1)2
3 = \sqrt (4-1)2 + (2-r)2
3 = \sqrt 32 + (2-r)2
3 = \sqrt 9 + 4 – 4r + r2
3 = \sqrt r2 - 4r + 13
9 = r2 - 4r + 13 By squaring both sides
r2 - 4r + 4 = 0
(r-2)(r-2) = 0
r = 2
Source: Myschool Past Questions Archive (Record #9335)