Multiply : \( (x^2 + y^2 + z^2 – xy + xz + yz) \) by \( (x + y – z) \)

\[ (x^2 + y^2 + z^2 – xy + xz + yz)(x + y – z) \] \[ = x^3 + x^2y – x^2z + xy^2 + y^3 – y^2z + xz^2 + yz^2 – z^3 \] \[ \quad – x^2y – xy^2 + xyz + x^2z + xyz – xz^2 + xyz + y^2z – yz^2 \] \[ = x^3 + y^3 – z^3 + 3xyz \]