Jika f(x)=x^3+5x^2+m dan f (-1).f (1)=f(2)+6, maka nilai m adalah

→ f(-1) = (-1)³+5(-1)²+m
⇔f(-1) = -1+5+m
⇔f(-1) = m+4

→ f(1) = 1³+5.1²+m
⇔f(1) = 1+5+m
⇔f(1) = m+6

→ f(2) = 2³+5.2²+m
⇔f(2) = 8+20+m
⇔f(2) = m+28

→ f(-1).f(1) = f(2)+6
⇔(m+4)(m+6) = m+28+6
⇔m²+10m+24 = m+34
⇔m²+9m-10 = 0
⇔(m+10)(m-1) = 0
⇔m = -10, 1

∴ m = -10 atau 1