Find the perimeter when 84 triangles are put together in the pattern shown below. Assume that all triangle sides are 1 cm long.

Answer:
86 cm.
Step-by-step explanation:
If we add 1 more triangle to one in the picture we that:
If we place 6 triangles together the perimeter will be 6 + 2 = 6
for 8 triangles the perimeter is 10 .
For 84 the perimeter will be 86 cm.
Here, we are required to determine the perimeter of 84 triangle arranged in the pattern as in the attached image.
Since , the triangles are equilateral triangles as all sides are 1cm long.
By observation; The perimeter of one of the triangles is : 3 × 1cm = 3cm.
Upon addition of a second triangle; the perimeter becomes; 4 × 1cm = 4cm.
And when a 3rd triangle is added, the perimeter becomes; 5 × 1cm = 5cm.
Therefore, the perimeter of the consecutive number of triangles can be modelled into an arithmetic progression (a.p) with;
T(n) = a + (n - 1)d
As a result; the 84th term is given as;
T(84) = 3 + (84 - 1) × 1
T(84) = 86cm
Therefore, the perimeter of 84 triangles arranged in that pattern is 86cm.
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