JAMB - Mathematics (2021 - No. 16)

P(-6, 1) and Q(6, 6) are the two ends of the diameter of a given circle. Calculate the radius.
6.5 units
13.0 units
3.5 units
7.0 units

Explanation

PQ\(^2\) = (x2 - x1)\(^2\) + (y2 - y1)\(^2\) 

= 12\(^2\)  + 5\(^2\) 
= 144 + 25
= 169

PQ = √169 = 13

But PQ = diameter = 2r, r = PQ/2 = 6.5 units

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