Garis y=mx + 4 menyinggung lingkaran x^2+y^2 = 4, carilah nilai m

Y= mx + 4 subs ke x² + y² = 4
x² + (mx+4)² = 4
x² + m²x² + 8 mx + 16 = 4
(1+m²) x² + (8m) x + 12 = 0
a =1+m²
b = 8m
c = 12
.
D = 0
D = b²-4ac
.
b² -4ac =0
b² = 4ac
(8m)²  = 4(1+m²)(12)
64 m²  = 48 + 48m² = 0
16m²= 48
m² = 3
m = √3  atau m = - √3