bonsoir
1) 5 X a + 2 X a + a X a = 5 a + 2 a + a² = a² + 7 a
2) 6 X a X a X 3 = 18 a²
3) (3x + 5 ) - (x - 6) = 3 x + 5 - x + 6 = 2 x + 11
4) 2x² + 5x + 4 - x² + 4 + 6x = x² + 11 x + 8
5) 1x(u + 4 X v) + (3u - v ) = u + 4 v + 3 u - v = 3 v + 4 u
6) dXd-dXdXd = d² - d ³