\(\displaystyle \eqalign{
& {\rm{a}})\,{x^6} + {x^2}{y^5} + x{y^6} + {x^2}{y^5} - x{y^6} \cr
& = {x^6} + (1 + 1){x^2}{y^5} + (1 - 1)x{y^6} \cr
& = {x^6} + 2{{\rm{x}}^2}{y^5} \cr} \)
b) \(\displaystyle {1 \over 2}{x^2}{y^3} - {x^2}{y^3} + 3{{\rm{x}}^2}{y^2}{z^2} \)\(- {z^4} - 3{{\rm{x}}^2}{y^2}{z^2}\)
\(\displaystyle = \left( {{1 \over 2} - 1} \right){x^2}{y^3} \)\(+ (3 - 3){x^2}{y^2}{z^2} - {z^4} \)
\(\displaystyle = - {1 \over 2}{x^2}{y^3} - {z^4}\)
