a: A={0;1;2;3;...;11;12}

A={x∈N|0<=x<=12}

b: B={1;3;5;7;9}

B={x∈N|x=2k+1, 0<=k<=4}

=1/5-1/6+1/6-1/7+1/7-...+1/9-1/10

=2/10-1/10=1/10

−14.15211+684.−111=−111(684+1524)=−111.2204=−5

a: =1/5+5/2x2/7

=1/5+5/7=7/35+25/35=32/35

b: =9x1/9-(-1/1000)*15/2

=1+15/2000=2015/2000

=>6|x+2|=18

=>|x+2|=3

=>x+2=-3 hoặc x+2=3

=>x=-5 hoặc x=1