2009
Mathematics
JAMB
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
Correct Answer: 2
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
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 = 2THIS WEEK's
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