JAMB 2001 · UME · Q29

Coordinate geometry

$P(-6, 1)$ and $Q(6, 6)$ are the two ends of a diameter of a given circle. Calculate the radius.

Worked solution (try it first)

The changes from $P$ to $Q$ are $6 - (-6) = 12$ and $6 - 1 = 5$ .
The diameter is $PQ = \sqrt{12^2 + 5^2} = \sqrt{169} = 13$ .
The radius is half the diameter: $6.5$ units, option B.

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