1) = x^6-x^4+x^3+x^4-x^2+x-x^3+x-1=x^6-x^2+2x-1
2) = c^6-c^5+c^4-c^2+c-c^5+c^4-c^3+c-1=c^6-2c^5+2c^4-c^3-c^2+2c-1
3) = (x^2-3x+7x-21)(x^2-2x-5)=x^4-2x^3-5x^2-3x^3+6x^2+15x+7x^3-14x^2-35x-21x^2+42x+105=x^4+2x^3-34x^2+22x+105
4) = (y^5+y^2+y-y^4-y-1)(y^8+y^5+1)=y^13+y^10+y^5+y^10+y^7+y^2-y^12-y^9-y^4-y^8-y^5-1=y^13-y^12+2y^10-y^9-y^8+y^7-y^4+y^2-1