Question

Tính S = 1² + 2² + 3² + ..... + 99²

Answer 1

S = 1² + 2² + ... + 99²

=> S = 1.1 + 2.2 + ... + 99.99

=> S = ( 1.2 + 2.3 + ... + 98.99 ) + ( 1 + 2 + ... + 99 )

=> S = 323400 + 4950

=> S = 328350

Answer 2

S=1²+2²+3²+..........+99²

S=1.(2-1)+2.(3-1)+..........+99.(100-1)

S=1.2-1+2.3-2+.........+99.100-99

S=(1.2+2.3+.......+99.100)-(1+2+..........+99)

S=333300-4950

S=328350

Answer 3

S=1²+2²+...+99²

=>S=1.1+2.2+...+99.99

=>S=(1.2+2.3+...+98.99)+(1+2+...99)

=>S=323400+4950

=>S=328350

đây là c1 , còn c2 bn tự tìm nhé