f'(x)=18*4x³-2x=72x³-2x=0
2x(36x²-1)=0
2x(6x-1)(6x+1)=0
x1=0
x2=1/6
x3=-1/6
x -1/6 0 1/6
f'(x) ----------------------0++++0----------0++++++++++++++++
f(x) ↓↓↓↓↓↓↓↓↓↓↓↓f(-1/6)↑↑↑5↓↓↓↓↓↓f(1/6)↑↑↑↑↑↑↑↑↑↑↑↑↑
Punctele de extrem sunt A(-1/6,359/72) , O(0,0) si B(1/6, 359/72)