Correct Answer: Option B

Explanation

A(4,2) and B(1,r), AB = 3 units

3 = √ (x2- x1)2 + (y2-y1)2


3 = √ (4-1)2 + (2-r)2


3 = √ 32 + (2-r)2


3 = √ 9 + 4 – 4r + r2


3 = √ r2 - 4r + 13

9 = r2 - 4r + 13 By squaring both sides
r2 - 4r + 4 = 0
(r-2)(r-2) = 0
r = 2

There is an explanation video available below.

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