Question

Tính tổng S = 1 x 2 + 2 x 3 + 3 x 4 + ........+99 x 100

 

Answer 1

3S=1x2x3+2x3x(4-1)+..............+99x100x(101-98)

3S=1x2x3+2x3x4-1x2x3+...........+99x100x101-98x99x100

3S=99x100x101

S=99x100x101:3

S=333300

Answer 2

3S=1*2*3+2*3*(4-1)+.....99*100*(101-98)

3S=1*2*3+2*3*4-1*2*3+99*100*101-98*99*100

3s=99*100*101=999900

S=999900:3=333300

 

Answer 3

ket qua = 333300