Nilai-nilai c agar salah satu akar persamaan x2 + cx + 8 = 0 dua kali akar lainnya adalah

x1 = 2x2
x1 . x2 = 8
2x2 . x2 = 8
x2^2 = 4
x2 = 2
x1 = 2(2) = 4

x1 + x2 = -c
4 + 2 = -c
6 = -c
c = -6

x1 = 2 . x2
x^2 + cx + 8 = 0
x1 . x2 = c/a
2 . x2 . x2 = 8/1
(x2)^2 = 8/2
x2 = ± √4 = ± 2

1) x2 = 2 => x1 = 2 (2) = 4
x1 + x2 = -b/a
4 + 2 = -c/1
6 = -c
c = -6

2) x2 = -2 => x1 = 2(-2) = -4
x1 + x2 = -b/a
-4 + (-2) = -c/1
c = 6