Tentukan jari - jari lingkaran x² + y² - 2x + 4y + 1 = 0...

x² + y² - 2x + 4y + 1 = 0
A = -2
a = -1/2 A = 2/2 = 1

B = 4
b = -1/2 B = -4/2 = -2

C = 1

Jari jari lingkaran
= √(a² + b² - C)
= √(1² + (-2)² - 1)
= √(1 + 4 - 1)
= √4
= 2

Bab Lingkaran
Matematika SMA Kelas XI

(x - h)² + (y - k)² = r²

x² + y² - 2x + 4y + 1 = 0
x² - 2x + y² + 4y = -1
(x - 1)² + (y + 2)² = - 1 + 1 + 4
(x - 1)² + (y + 2)² = 4

r² = 4
r = 2