This is an onerous question unless you are permitted to use a graphing calculator.
My graphing calculator gives roots of 1.88 and .53 and 2 complex roots.
The single minimum point occurs at approximately x=1.5 and the minimum is approximately -1.5
Without a graphing calculator you could make a rough graph by hand and use Newton' method with first guess of x=2 or you could use Horner's method for irrational roots with the same first guess.