Question

Tính :

        S = 1.2+2.3+3.4+....+15.16

 

Answer 1

S = 1.2 + 2.3 + 3.4 + ... + 15.16

3S = 1.2.(3-0) + 2.3.(4-1) + 3.4.(5-2) + ... +15.16.(17-14)

3S = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 15.16.17 - 14.15.16

3S = 15.16.17

S = 5.16.17

S = 1360

Answer 2

Bạn nào làm nhanh nhất cho mình cho 2 k !!!

Answer 3

3S=1.2.3+2.3.3+3.4.3+...+15.16.3

3S=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+...+15.16.(17-14)

3S=0.1.2 - 1.2.3+1.2.3-2.3.4+2.3.4-3.4.5+...+14.15.16-15.16.17

3S=15.16.17

3S=4080

S=4080:3=1360