Differentiate:

$P(x)=a{x}^3+bx$

$P^{\text{'}}(x)=3ax+b$

$P^{\text{'}}(x)=a{x}^2+bx$

$P^{\text{'}}(x)=3a{x}^2-b$

$P^{\text{'}}(x)=3a{x}^2+b$