agar garis y=x+c menyinggung lingkaran x^+y^=25 maka nilai c adalah

x^2 + y^2 = 25
x^2 + (x + c)^2 = 25
x^2 + x^2 + 2cx + c^2 - 25 = 0
2x^2 + 2cx + (c^2 - 25) = 0

p = 2
q = 2c
r = c^2 - 25

q^2 - 4pr = 0
(2c)^2 - 4(2)(c^2 - 25) = 0
4c^2 - 8(c^2 - 25) = 0
4c^2 - 8c^2 + 200 = 0
-4c^2 = -200
4c^2 = 200
c^2 = 50
c = ±√50
c = ±5√2