nilai nilai c agar salah satu akar persamaan x2+cx+8=0 dua kali akar lain nya adalah

[tex]x_{1}=2x_{2}[/tex]

[tex]x_{1}*x_{2}=\frac{c}{a}[/tex]
[tex]2x_{2}*x_{2}=\frac{8}{1}[/tex]
[tex]2(x_{2})^{2}=8[/tex]
[tex](x_{2})^2=4[/tex]
[tex]x_{2}=2[/tex] atau [tex]x_{2}=-2[/tex]
[tex]x_{1}=4[/tex] atau [tex]x_{1}=-4[/tex]

kasus 1:
[tex]x_{1}+x_{2}=\frac{-b}{a}[/tex]
[tex]6=\frac{-c}{1}[/tex]
[tex]c=-6[/tex]

kasus 2:
[tex]x_{1}+x_{2}=\frac{b}{a}[/tex]
[tex]-6=\frac{-c}{1}[/tex]
[tex]c=6[/tex]

Jika diketahui x1 = n x2 maka berlaku rumus : nb^2 = (n + 1)^2 . ac
x^2 + cx + 8 = 0 ==> a = 1, b = c, c = 8
x1 = 2 x2 ==> n = 2
nb^2 = (n + 1)^2 . ac
2 . c^2 = (2 + 1)^2 . 1 . 8
2c^2 = 9 . 8
c^2 = 36
c = ± 6
c = 6 atau c = 6