\[\boxed{\text{978.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (x + y)^{6} + (x - y)^{6} =\]
\[= x^{6} + 6x^{5}y + 15x^{4}y^{2} +\]
\[+ 20x^{3}y^{3} + 15x^{2}y^{4} + 6xy^{5} +\]
\[+ y^{6} + x^{6} - 6x^{5}y -\]
\[- 15x^{4}y^{2} - 20x^{3}y^{3} + 15x^{2}y^{4} -\]
\[- 6xy^{5} + y^{6} = 2x^{6} + 30x^{4}y^{2} +\]
\[+ 30x^{2}y^{4} + 2y^{6}\]
\[\textbf{б)}\ (x + y)^{6} - (x - y)^{6} =\]
\[= x^{6} + 6x^{5}y + 15x^{4}y^{2} +\]
\[+ 20x^{3}y^{3} + 15x^{2}y^{4} + 6xy^{5} +\]
\[+ y^{6} - x^{6} + 6x^{5}y -\]
\[- 15x^{4}y^{2} + 20x^{3}y^{3} - 15x^{2}y^{4} +\]
\[+ 6xy^{5} - y^{6} = 12x^{5}y +\]
\[+ 40x^{3}y^{3} + 12xy^{5}\]