函數f(x)=x^3+2x^2-ax+3既有極小值又有極大值,則a的取值範圍為?

函數f(x)=x^3+2x^2-ax+3既有極小值又有極大值,則a的取值範圍為?

f(x)=x^3+2x^2-ax+3
f'(x)= 3x^2 + 4x - a
f'(x)= 0
3x^2 + 4x - a =0
△>0
16+ 12a > 0
a > -4/3