Question 3
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.
1 3 6
15
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)
10
Part A
Prove the statement is true for n = 1.