Hmm. This is tough using only algebra. You can get a solution graphically by checking for where the graph changes direction.
This will show that we have
min at (-1.57,-2.88)
max at (0.07,6.04)
min at (2.25,-12.95)
how do I find the relative maximum and minimum values of x^4-x^3-7x^2+x+6
2 answers
x-3
____
-2x-3
____
-2x-3