Question 11(ii)
Fig. below gives a matchstick pattern of triangles. As in Exercise 11(a) above, find the general rule that gives the number of matchsticks in terms of the number of triangles.
The column of 'number of matchsticks - 1' forms the multiplication table of 2. i.e., 2, 4, 6, 8, ...
Let the number of triangles be x.
The number of matchsticks used in each pattern is 1 more than 2 times the number of triangles in it.
∴The number of matchsticks used in each pattern = 2x+1.