a)
[tex] - 2x + ( - 6xy + 4x - y) = - 2x - 6xy + 4x - y = - 6xy + 2x - y[/tex]
b)
[tex]k - ( - 2k + 8m - 3km) = k + 2k - 8m + 3km = 3k - 8m + 3km[/tex]
c)
[tex] - 6xy - (2xy - 3x + 4y) = - 6xy - 2xy + 3x - 4y = - 8xy + 3x - 4y[/tex]
d)
[tex]9a + 4c - (8c - 2a) = 9a + 4c - 8c + 2a = 11a - 4c[/tex]