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![](https://rs.olm.vn/images/avt/0.png?1311)
A có 100 số hạng
Tổng A :
( 100 + 1 ) x 100 : 2 = 5050 \(⋮\)5
=> A \(⋮\)5
![](https://rs.olm.vn/images/avt/0.png?1311)
Đáp án cần chọn là: A
Ta có
90–85 +80–75+70–65+60–55+50–45
=5+5+5+5+5=10+10+5=25.
![](https://rs.olm.vn/images/avt/0.png?1311)
1-2-3-4-...-91-92-93-94-95-96-97-98-99=1-(2+3+4+5+..+97+98+99)
=1-[(2+99).(99-2+1):2]
=1-(101*98:2)
=1-4949
=-4948
![](https://rs.olm.vn/images/avt/0.png?1311)
\(100-94+90-84+80-74+70-64+60-54\)
\(=6+6+6+6+6\)
\(=6^5=30\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(100-94+90-84+80-74+70-64+60-54\)
\(=6+6+6+6+6\)
\(=6.5=30\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(-70+70\)
\(=-\left(70-70\right)\)
\(=-0\)
\(=0\)
c) \(\left(-11\right)+\left(-22\right)+\left(-33\right)\)
\(=-11-22-33\)
\(=-\left(11+22\right)-33\)
\(=-33-33\)
\(=-\left(33+33\right)\)
\(=-66\)
d) \(-840+560+\left(-160\right)\)
\(=-840+560-160\)
\(=-\left(840-560\right)-160\)
\(=-280-160\)
\(=-\left(280+160\right)\)
\(=-440\)
\(-99+98+\left(-97\right)+96+\left(-95\right)+94+\left(-93\right)+92+\left(-91\right)+90\)
\(=-99+98-97+96-95+94-93+92-91+90\)
\(=-\left(99-98\right)-\left(97-96\right)-\left(95-94\right)-\left(93-92\right)-\left(91-90\right)\)
\(=-1-1-1-1-1\)
\(=-\left(1+1\right)-1-1-1\)
\(=-2-1-1-1\)
\(=-\left(2+1\right)-1-1\)
\(=-3-1-1\)
\(=-\left(3+1\right)-1\)
\(=-4-1\)
\(=-\left(4+1\right)\)
\(=-5\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Trả lời
90-80+70=80
60-98+95=57
45+90-92=43
Học tốt, đăng nhiều thế !
Trả lời :
90 - 80 + 70 = 80
60 - 98 + 95 = 57
45 + 90 - 92 = 43
Học tốt