Agar garis x -y +p menyinggung lingkaran x2 +y2 - 2x - 7 = 0 maka P harus lah

jawab

x - y + p = 0
y = x + p

x² +(x +p)² - 2x - 7 = 0
x² + x² + 2px + p²  -2x - 7 = 0
2x² + (2p-2)x + (p² -7) = 0
D= 0
(2p - 2)² - 4(2)(p² -7) = 0
4p² - 8p + 4 - 8p² + 56 = 0
-4p² - 8p  + 60 = 0
p² + 2p  - 15 =0
( p  + 5)(p - 3)=0
p = - 5
p =  3