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![](https://rs.olm.vn/images/avt/0.png?1311)
) 1 - 2 - 3 + 4 + 5 - 6 - 7 + 8 + ... + 97 - 98 - 99 + 100 ( có 100 số; 100 chia hết cho 4)
= (1 - 2 - 3 + 4) + (5 - 6 - 7 + 8) + ... + (97 - 98 - 99 + 100)
= 0 + 0 + ... + 0
= 0
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) =(1-2)+(3-4)+...........+(199-200)
=-1+ -1+ -1........+ -1(100 lần -1)
=-100
b)=1+3-2+5-4+7-6+.......+99-98-100
1+(1+1+1+1+1........+1)-100=.......(trong ngoac co 49 so 1 vi 49.2+1=99
=1+49-100=-50
k cho minh nhe!
☺☺☺☺☺☺
![](https://rs.olm.vn/images/avt/0.png?1311)
cho mi sửa lại:
\(a) A = 1^2+2^3+3^4+...+2014^{2015} b) B = 101^2+102^2+...+199^2+200^2 c) C = 1^3+2^4+3^5+4^6+...+99^{101}+100^{102}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
A = 1*2*3 + 2*3*4 + 3*4*5 ... + 99*100*101
=> 4A = 1*2*3*4 + 2*3*4*4 + 3*4*5*4 + ... +99*100*101*4
=> 4A = 1*2*3*4 + 2*3*4*(5 - 1) + 3*4*5*( 6 - 2) + ... + 99*100*101*(102 - 98)
=> 4A = 1*2*3*4 + 2*3*4*5 - 1*2*3*4 + 3*4*5*6 - 2*3*4*5 + ... + 99*100*101*102 - 98*99*100*101
=> 4A = 99*100*101*102
=> 4A = 101989800
=> A = 25497450
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(\text{ a)(-14).(-125).(+3).(-8)}\)
\(=\left[\left(-14\right).\left(+3\right)\right].\left[\left(-125\right).\left(-8\right)\right]\)
\(=\left(-42\right).1000\)
\(=-42000\)
\(b)\left(-127\right).57+\left(-127\right).43\)
\(=\left(-127\right).\left(57+43\right)\)
\(=\left(-127\right).100\)
\(=-12700\)
\(c)\left(-13\right).34-87.34\)
\(=34.\left[\left(-13\right)-87\right]\)
\(=34.\left(-100\right)\)
\(=-3400\)
#Mạt Mạt#