a) \(31+32+33+34+35-11-12-13-14-15\)
\(=\left(31-11\right)+\left(32-12\right)+\left(33-13\right)+\left(34-14\right)+\left(35-15\right)\)
\(=20+20+20+20+20\)
\(=100\)
b) \(357-1284+1280-1357\)
\(=\left(357-1357\right)+\left(-1284+1280\right)\)
\(=-1000-4\)
\(=-1004\)
c) \(1+2-3-4+5+6-7-8+...-79-80+81\)
\(=\left(1+2-3-4\right)+\left(5+6-7-8\right)+...+\left(77+78-79-80\right)+81\)
\(=-4+\left(-4\right)+...+\left(-4\right)+81\) (\(20\) số \(-4\))
\(=-4.20+81\)
\(=-80+81\)
\(=1\)
d) \(1-4-7+10+13-16-19+22-25+28+31-34+37\)
\(=\left(1-4-7+10\right)+\left(13-16-19+22\right)+\left(-25+28+31-34\right)+37\)
\(=0+0+0+37\)
\(=37\)
Đúng 1
Bình luận (0)
