Question

Tính a= 1² + 2²+ 3²+ .... + 99² + 100^{2.                       B= 1.2+2.3+3.4+....+99.100}

 

Answer 1

B = 1.2 + 2.3 + 3.4 + ... + 99.100 

3B = 1.2.3 + 2.3.(4-1) + 3.4.(5-2) + ... + 99.100.(101-98)

3B = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 99.100.101 - 98.99.100

3B = 99.100.101

  B = \(\frac{99.100.101}{3}=333300\)