Finding Local Extrema in Polynomial Equations

[alex123aaa]

how can i find the x-coordinates of all local extrema in this equations please anyone could answer it for me?

f(x)=x^3+4x^2+2x

f(x)=x^4-3x^2+2x

f(x)=x^5-2x^2-4x

f(x)=x^5+4x^2-4x

 

[Mark44]

Please read the Forum Rules here https://www.physicsforums.com/showthread.php?t=5374, particularly the section on Homework. No one is likely to answer these for you without you exerting some effort first.