lingkaran x^2+y^2-8x-10y+16=0 menyinggung sumbu x di titik

x^2 -8x +16 -16 + y^2 - 10y +25-25 +16 = 0
(x-4)^2 + (y-5)^2 -16-25+16 = 0
(x-4)^2 + (y-5)^2 -25 = 0
(x-4)^2 + (y-5)^2 = 25
jadi pusat (4,5)