Question

Construct an equilateral triangle whose perimeter
is 15 cm?

Answer 1

First of all draw a 5cm line as all the sides of equilateral triangle is same so 15/3= 5cms
Then take a protractor and fix it at the one extreme side of your line have a 5cm measured on it draw an arc repeat this with other extreme side you will get a point where both the arc will coincide or have fix point take a scale and join those extreme points with the created one . Done

Answer 2

15 divided by 3 i.e. 5cm each side,
steps of construction:
1.draw a base of 5 cm
2.then take 5 cm on your rounder keep the pointed end on one end of the base you drawn and cut an arc...in the center
3.now do the same with other point
4.join the lines where the arc is cut
just like in photo
ignore the lengths just see how the arcs are drawn