Lesben F(x)=x²/((3x+1) , x≠-1/3
(u/v)´=(u´v-uv´)/v²

f´(x)=(2x(3x+1)-x².3)/(3x+1)²=(6x²+2x-3x²)/(3x+1)²=
=(3x²+2x)/(3x+1)²

mikael2 Y=x²/(3x+1)
y=u/v  y'=1/v²[u'v-v'u]
u=x²    u'=2x    v=(3x+1)  v'=3
y'=1/(3x+1)²[2x(3x+1)-3*x²]=1/(3x+1)²[3x²+2x]