JAMB - Mathematics (2001 - No. 19)

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\(^2\) = (x\(_2\) - x\(_1\))\(^2\) + (y\(_2\) - y\(_1\))\(^2\) 
= 12\(^2\)  + 5\(^2\) 
= 144 + 25
= 169
PQ = \(\sqrt{169}\) = 13
But PQ = diameter = 2r, r = \(\frac{\text{PQ}}{2}\) = 6.5 units

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