Create a geometric argument that more clearly shows that 2tn

Create a geometric argument that more clearly shows that 2t_n = (n + 1) n.

This formula shows a series whose common difference is an Arithmetic Progression.

for example if we put n=0 the value of t₀=0

n=1, t₀=1

n=2, t₀=3

n=3,t₀=6

n=4,t₀=10

n=5,t₀=15

n=6, t₀=21

sand so on , therefore the series becomes 0,1,3,6,10,15,21......

if you see the difference the difference is an AP i.e 1,2,3,4,5,6,......

therefore formula for AP =>

a_n=a+(n-1)d

a_n= nth term

a= first term

d= common difference