Răspuns:
[tex]a)3(a + b) - x(a + b) = \\ = (a + b)(3 - x)[/tex]
[tex]b)( {x}^{2} + {y}^{2} ) \times a + b( {x}^{2} + {y}^{2} ) = ( {x}^{2} + {y}^{2} )(a + b)[/tex]
[tex]c)a(m + n) - b(m + n) = (m + n)(a - b)[/tex]
[tex]d)2m(2m - 1) - (2m - 1) = (2m - 1) \times 2m + 1[/tex]