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What is the radius of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0? units

• This topic was modified 2 years, 1 month ago by ProtonsTalk.
• This topic was modified 2 years, 1 month ago by ProtonsTalk.
#20941
ProtonsTalk
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The radius of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0 is 5 units.

We know that the general form of a circle is as follows.

(x – a)2 + (y-b)2 = r2

=> x2 + y– 2ax – 2by + (a2 + b2 – r2) = 0

And we know that radius = r = √(a2 +b2 )

So, comparing the given equation and the general form of the equation.

we get

=> -2ax = 8x => a = – 4

=> -2by = -6y => b = 3

So, r = √((-4)2 +32 ) = √16 + 9 = √25 = 5

So, the radius r of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0 is 5 units.

• This reply was modified 2 years, 1 month ago by ProtonsTalk.
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