Persamaan garis singgung pada lingkaran x²+y²-4x+2y-4=0 yang tegak lurus dengan garis 4x+3y+1=0 adalah

x² + y² - 4x + 2y - 4 = 0
A = -4, B = 2 dan C = -4
pusat = (-A/2, -B/2) = (2, -1)
r = √(2² + (-1)² - C) = √(4 + 1 + 4) = 3
4x + 3y + 1 = 0 → 3y = -4x - 1
y = -(4/3)x - 1/3 → m = -4/3
tgk lurus → m1 = -1/m = -1/-(4/3) = 3/4
y - b = m1(x - a) ± r√(1 + m1²)
y + 1 = (3/4)(x - 2) ± 3√(1 + (3/4)²)
4y + 4 = 3(x - 2) ± 15
PGS
4y = 3x - 10 ± 15