The first five triangular numbers are shown, where n represents the number of dots in the base of the figure, and d(n) represents the total number of dots in the figure.

When n = 1, there is 1 dot. When n = 2, there are 3 dots. When n = 3, there are 6 dots. Notice that the total
number of dots d(n) increases by n each time.

Use induction to prove that
d (n) = n(n+1)/2

Prove the statement is true for n = 1.