Cho a = –13; b = 25; c = –30. Tính giá trị biểu thức:

a) a + a + 12 – b.

b) a + b – (c + b).

c) 25 + a – (b + c) – a.

a) a + a + 12 – b = 2a + 12 – b = 2.(–13) + 12 – 25 = –26 + 12 – 25 = –29.

b) a + b – (c + b) = a + b – c – b = a – c = –13 – (–30) = 30 – 13 = 17.

c) 25 + a – (b + c) – a = 25 – b – c = 25 – 25 – (–30) = 30.