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

The numbers 1,3,6,10 and 15 are represented in the form of a triangle with dots.

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

Use induction to prove that .