Question

S=1.2+2.3+3.4+.............+n(n+1)

Answer 1

S=1.2+2.3+3.4+.....+N(N+1)

3S=1.2(3-0)+2.3(4-1)+....+N.(N+1)+N(N+1)-(N+2)

3S=1.2.3+2.3.4+3.4.5+.+N(N+1)+(N+2)

3S=N(N+1)+(N+2)

S=N(N+1)+(N+2)/3

Answer 2

3.A=1.2.(3-0)+2.3.(4-1)+3.4.(5 -2)...+ n.(n+1) . ((n+2) - (n-1)) 
3.A=1.2.3+2.3.4+3.4.5+...+ (n-1) . n. (n+1)+ n. (n+1). (n+2) - 
0.1.2 -1.2.3 -2.3.4 -3.4.5 -...(n-1)n(n+1) 
3A=n.(n+1).(n+2) 
A=n.(n+1).(n+2)\3 

Ai tk mình mk tk lại nha

Answer 3

Rảnh v~