Using I forgot who's thingummy math thing change sign thing ah, descartes rule of signs, thank you google
replace x with -x simplify count the number of times the sign changes between terms if the number is 2 or more, keep subtracting 2 until you reach 0 or 1 so
if we replace x with -x we get -x^5+2x^3+7x^2-2x-2 (-), (+), (+), (-), (-) 2 changes 2-2=0
