The figure is made of identical triangles.
- Complete the table for layers 10 and 15.
- If each small triangle has a height of 4 cm and a perpendicular base of 2 cm, find the area of all the triangles at the 30th layer.
Layer number |
Number of triangles |
1 |
1 |
2 |
3 |
3 |
5 |
4 |
7 |
... |
... |
10 |
(i) |
... |
... |
15 |
(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 15
= 15 + (15 - 1)
= 15 + 14
= 29
(b)
Number of triangles in the 30th layer
= 30 + (30 - 1)
= 30 + 29
= 59
Area of one small triangle
=
12 x 4 x 2
= 4 cm
2Area of all the triangles at the 30th layer
= 4 x 59
= 236 cm
2 Answer(s): (a) 19, 29; (b) 236 cm
2