Let us put a circle of radius 5 on a graph. Now let's work out exactly where all the points are.
We make a right-angled triangle: 52+ 02= 25 + 0 = 253432+ 42= 9 + 16 = 250502+ 52= 0 + 25 = 25−4−3(−4)2+ (−3)2= 16 + 9 = 250−502+ (−5)2= 0 + 25 = 25
Start with:x2 + y2 = r2
Values we know:22 + y2 = 52
Rearrange:y2 = 52 − 22
Square root both sides:y = ±√(52 − 22)
Solve:y = ±√21
y ≈ ±4.58...

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