Asquare has the sides length 2k-1 units. an equilateral triangle has the sides of the length k+2 units. the square and the triangle have the same perimeter. what is the value of k? i got k=3 i think i got wrong can someone correct

I think that you assumed that:
2k - 1 = k + 2

However we can't do this, because a square has 4 sides whilst a triangle only has 3 sides. 
This means that we can say
4(2k - 1) = 3(k + 2) 

We multiply by 4 due to 4 sides of the square, and by 3 due to the 4 sides of the triangle.

Lets expand the brackets, and solve it:

4(2k - 1) = 3(k + 2)
8k -4 = 3k + 6
5k -4 = 6    ( subtract both sides by 3x to collect the x values)
5k = 10      (add both sides by 4 to get the x's alone)
k = 2           (divide both sides by 5 to get what just x is)

So k = 2 units

Use photo math it it’s so good