Jari jari lingkaran x^2 + y^2 + 4x + 12y - 9=0 adalah

x^2 + y^2 + 4x + 12y - 9 = 0
(x + 2)^2 + (y + 6)^2 - 4 - 36 - 9 = 0
(x + 2)^2 + (y + 6)^2 = 49

r^2 = 49
r = 7

x²+y²+4x+12y-9=0
pusat = (a,b) = (-½A,-½B) = (-2,-6)
C = -9

r = √(a²+b²-C)
= √[(-2)²+(-6)²-(-9)]
= √(4+36+9)
= √49
= 7