Salah satu persamaan garis singgung lingkaran x2+y2-4x-10y+9=0 yang tegak lurus garis 2x-y-10=0

A=-4 B=-10 C=9
O (a,b) = (-A/2, -B/2) = (2,5)
r = √(2²+5²-9 = √20

tegak lurus garis 2x-y-10 = 0
m = -2
mgs = -1 ÷ -2 = 1/2

y-b = m(x-a) ± r√mgs²+1
y-5 = 1/2(x-2) ± √20 √5/4
y-5 = 1/2x - 1 ± 5
1. y = 1/2x +9 atau 1/2x-y+9 = 0
2. y = 1/2x -1 atau 1/2x-y-1 = 0