Question

Tính A=1.2.3+2.3.4+,,,,,,+98.99.100

Answer 1

Ta có: A=1.2.3+2.3.4+…+98.99.100

=>A.4=1.2.3.4+2.3.4.4+…+98.99.100.4

=>A.4=1.2.3.(4-0)+2.3.4.(5-1)+…+98.99.100.(101-97)

=>A.4=1.2.3.4-0.1.2.3+2.3.4.5-1.2.3.4+…+98.99.100.101-97.98.99.100

=>A.4=98.99.100.101

=>A.4=97990200

=>A=97990200:4

=>A=24497550

Answer 2

Michiel Girl Mít ướt bài lớp 7 đó, lm đi

Answer 3

CT:  

1.2.3...a+2.3.4...(a+1)+......+(n+1)(n+2)....(n+a)

=\(\frac{\left(n+1\right)\left(n+2\right).....\left(n+a+1\right)}{a+1}\)