Penyelesaian persamaan garis singgung lingkaran:
x² + y² – 6x + 10y – 91 = 0 ➞ a = 3, b = -5, c = -91 lewat titik (-7, -10) ➞ x₁ = -7, y₁ = -10
xx₁ + yy₁ – a(x + x₁) – b(y + y₁) + c = 0
-7x – 10y – 3(x – 7) + 5(y – 10) – 91 = 0
-7x – 10y – 3x + 21 + 5y – 50 – 91 = 0
-10x – 5y – 120 = 0
2x + y + 24 = 0