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Problem 4 - Entrance Test

A circle touches the y-axis at (0,4) and cuts the x-axis in two points whose distance apart is 6. Its radius is

Correct: C

Let centre (h,4). Touching y-axis gives |h| = r. Chord length 6 on x-axis: 2√{r²-4²}=6 → r²-16=9 → r=5.