# hatunhien giúp em nhé : Bài 1. Chứng tỏ : 1 / ( a – b + c ) – ( a + c ) = – b 2 / ( a + b ) – ( b – a ) + c = 2a + c 3 / – ( a + b – c ) + ( a – b –

1) $(a – b + c) – (a + c) = a – b + c – a – c = -b$

2) $(a + b) – (b – a) + c = a + b – b + a + c = 2a + c$

3) $ -(a + b – c) + (a – b – c) = -a – b + c + a – b – c = -2b$

4) $a(b + c) – a(b + d) = ab + ac – ab – ad = a(c – d)$

5) $a(b – c) + a(d + c) = ab – ac + ad + ac = a(b + d)$