a) 1 - 2 + 3 - 4 + 5 - 6 +.....+ 2017 - 2018 + 2019
b) 1 - 4 + 7 - 10 +.....+ 307 - 310 + 313
c) ( x2 - 4 ) . ( x2 - 10 ) < 0
d) ( x-1 ) . ( x2 - 4 ) = 0
e) -12 . ( x - 5 ) + 7 . ( 3 . x ) = 9
f) 27 - ( 5 - | x | ) = 31
g) -13 - ( 6 - | x + 1 | ) = 24