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

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.