The figure is made of identical triangles.
- Complete the table for layers 10 and 13.
- If each small triangle has a height of 5 cm and a perpendicular base of 2 cm, find the area of all the triangles at the 26th layer.
Layer number |
Number of triangles |
1 |
1 |
2 |
3 |
3 |
5 |
4 |
7 |
... |
... |
10 |
(i) |
... |
... |
13 |
(ii) |
(a)
1st layer: 0 + 1 = 1 triangle
2nd layer: 1 + 2 = 3 triangles
3rd layer: 2 + 3 = 5 triangles
4th layer: 3 + 4 = 7 triangles
Formula:
Number of triangles in a layer = Pattern number + (Pattern number - 1)
Number of triangles for layer 10
= 10 + (10 - 1)
= 10 + 9
= 19
Number of triangles for layer 13
= 13 + (13 - 1)
= 13 + 12
= 25
(b)
Number of triangles in the 26th layer
= 26 + (26 - 1)
= 26 + 25
= 51
Area of one small triangle
=
12 x 5 x 2
= 5 cm
2Area of all the triangles at the 26th layer
= 5 x 51
= 255 cm
2 Answer(s): (a) 19, 25; (b) 255 cm
2