Question

Persamaan kuadrat nx(pangkat 2) - 15x - 8=0 mempunyai akar a dan b. jika a=8,nilai ab = .... ??
tolong pakai rumus

Answer 1

Nx^2 - 15x - 8 = 0   karena x = 8
64n - 120 - 8 = 0
64n = 128
n = 2

2x^2 - 15x - 8 = 0
(x-8)(2x+1) = 0
x = 8  /  x = -1/2

ab = 8.-1/2
     = -4

Answer 2

Nx²-15x-8 = 0

mis :
akar"nya
α dan β
α = 8

maka,
α+β = 15/n
α×β = -8/n

α×β = -8/n
8×β = -8/n
8β  = -8/n
    n = -1/β

α+β = 15/n
8+β = 15/n
   n = 15/8+β
-1/β = 15/8+β
-8-β = 15β
-8    = 16β
    β = -1/2

jadi,
αβ = (8) × (-1/2)
    = -4