Question

 

A=1.2.3+3.4.5+5.6.7+........+98.99.100

Xin mọi người giúp mình

Answer 1

Bấm máy tính là ra liền

Answer 2

Đặt A=1.2.3+2.3.4+3.4.5+4.5.6+...+98.99.100

4A=(1.2.3+2.3.4+3.4.5+4.5.6+...+98.99.100)4

4A=1.2.3(4-0)+2.3.4(5-1)+3.4.5(6-2)+4.5.6(7-3)+...+98.99.100(101-97)

4A=1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+4.5.6.7-3.4.5.6+...+98.99.100.101-97.98.99.100

4A=1.2.3.4-1.2.3.4+2.3.4.5-2.3.4.5+3.4.5.6-3.4.5.6+...+97.98.99.100-97.98.99.100+98.99.100.101

4A=98.99.100.101

=>A=98.99.100.101/4

Answer 3

A = 1.2.3 + 2.3.4 + ... + 98.99.100

4A = 1.2.3.4 + 2.3.4.(5-1) + ... + 98.99.100.(101-97)

4A = 1.2.3.4 + 2.3.4.5 - 1.2.3.4 + ... + 98.99.100.101 - 97.98.99.100

4A = 98.99.100.101

4A = 97990200

A = 24497550

Answer 4

Ta có :

A = 1.2.3 + 2.3.4 + ... + 98.99.100

4A = 1.2.3.4 + 2.3.4.(5-1) + ... + 98.99.100.(101-97)

4A = 1.2.3.4 + 2.3.4.5 - 1.2.3.4 + ... + 98.99.100.101 - 97.98.99.100

4A = 98.99.100.101

4A = 97990200

A = 24497550

hok tốt