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8) persamaan garis singgung x^2 + y^2 = r^2 di titik (x1, y1) adalah
x1x + y1y = r^2 jadi pers garis singgung x^2 + y^2 = 41 di titik (-5, 4) :
-5x + 4y = 41
-5x + 4y - 41 = 0
5x - 4y + 41 = 0

10) x^2 + y^2 - 4x + 6y - 4 = 0
Pusat (a,b) = (-4/-2, 6/-2) = (2, -3)
Jari-jari : r = √(2^2 + (-3)^2 - (-4)) = √(4 + 9 + 4) = √17
Gradien : m = 4
Persamaan garis singgung
y - b = m(x - a) ± r√(m^2 + 1)
y - (-3) = 4(x - 2) ± √17 √(4^2 + 1)
y + 3 = 4x - 8 ± √17√17
y = 4x - 11 ± 17
y = 4x - 11 + 17 => y = 4x + 6
y = 4x - 11 - 17 => y = 4x - 28

9) x^2 + y^2 - 2x + 4y - 4 = 0
Pusat : (a, b) = (-2/-2, 4/-2) = (1, -2)
Jari-jari : r = √(1^2 + (-2)^2 - (-4)) = √(1 + 4 + 4) = √9 = 3
5x - 12y + 15 = 0 => m = -a/b = -5/-12 = 5/12 karena tegak lurus
maka m = -12/5
Persamaan garis singgung
y - b = m(x - a) ± r√(m^2 + 1)
y - (-2) = -12/5 (x - 1) ± 3 √(144/25 + 1)
y + 2 = -12/5 x + 12/5 ± 3 √(169/25)
y + 2 = -12/5 x + 12/5 ± 3 . 13/5 =====> kali 5
5y + 10 = -12x + 12 ± 39
12x + 5y - 2 ± 39 = 0
12x + 5y - 41 = 0 atau 12x + 5y + 37 = 0