Find the equation of a circle having its center at and a radius of length 4 units.
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The standard form of the equation of a circle is ( x − h ) 2 + ( y − k ) 2 = r 2 . Substituting − 3 for h , 5 for k and 4 for r in the standard form and simplfying, we obtain
( x − ( − 3 ) ) 2 + ( y − 5 ) 2 = 4 2
( x + 3 ) 2 + ( y − 5 ) 2 = 4 2
x 2 + 6 x + 9 + y 2 − 1 0 y + 2 5 = 1 6
x 2 + y 2 + 6 x − 1 0 y + 1 8 = 0