a)(a + b - c) - (b - c + d)
=a + b - c - b + c - d
=a + (b - b) -(c + c) - d
=a + 0 - c2 - d
b)- (a - b + c) + (a - b + d)
=-a + b - c + a - b + d
=(-a + a) + (b - b) - c + d
=0 + 0 - c + d
c) -(a + b) - (-a - b + c)
=-a - b + a + b - c
=(-a + a) - (b + b) - c
=0 - b2 - c
d)(a - b) - (c - d) - (a - c)
=a - b - c + d - a + c
=(a - a) - b - (c + c) + d
=0 - b - c2 + dd
Mỏi cả tay😧