Answer:
Tn=12n(n+1)
Step-by-step explanation:
Step-by-step explanation:
These are the triangular numbers - each term in the sequence being the sum of the first n positive integers:
T1=1=1
T2=3=1+2
T3=6=1+2+3
etc.
Notice that:
2Tn=(0)+1+(0)+2+...+(n−1)+(0)+n
2Tn+(0)+n+(n−1)+...+(0)+2+(0)+1
2Tn=(n+1)+(n+1)+...+(n+1)+(n+1)
2Tn=n(n+1)
So:
Tn=12n(n+1)