Which of the following is an odd function?
a) f(x)=3x2+x
b)f(x)=4x3+7
c)f(x)5x2+9
d)f(x)=6x3+2x

Hello : 
odd function is :  d)  f(x)=6x3+2x
because for all x in R  : f(-x) = 6(-x)3 +2(-x)
                                             = -6x3-2x(-x)3= -x3
                                             = -(6x3+2x)
f(-x) = -f(x)