câu 1:
a) 127-18(5+6)
=127-18.11
=127-198
=-71
b) 26+(4-12)
=26-8
=18
câu 2:
a) x-9=-14
x=-14+9
x=-5
b) (2x-8).2=24
4x-16=24
4x=24+16
4x=40
x=10
câu 3:
a) U(8)={1;-1;2;-2;4;-4;8;-8}
b)B{11}={11;22;33;44;55;...}
Câu 4:
1-2+3-4+5-6+...+99-100
=(1-2)+(3-4)+...+(99-100)
=-1-1-1-1...-1 (50 số -1)
=-50