Lingkaran x^2+y^2+8x-2y+a=0 r=6 nilai a

Lingkaran.

x² + y² + Ax + By + C = 0
r = √(1/4 A² + 1/4 B² - C)

x² + y² + 8x - 2y + a = 0
6 = √[1/4 (8)² + 1/4 (-2)² - a]
36 = 16 + 1 - a
a = -19