Rút gọn biểu thức sau :
a) (a2 +a- 1) ( a2 - a+1)
b) ( a+2) (a -2) ( a2+ 2a +4) ( a2- 2a +4)
c) (x-2)2 -(x - 3) (x-1)
d) (x-1)3 - (x+1)3 + 6(x+1) (x -1)
e) (2 +3y)2- ( 2x- 3y)2 - 12xy
g) (x+ 1)3 - (x-1 )3- (x3 -1 )- (x- 1)(x2 +x +1)
h) (x+1) (x2 -x+ 1)-( x-1) (x2 + x +1 )