In a square all 4 sides are equal, so when you cut it along the diagonal to make a triangle, both the base and the height of the triangle would be the same.
The area of a triangle is found by the formula 1/2 x base x height
Since the base and height are the same the formula becomes Area = 1/2 x S^2 ( where S is the length of a side).
The area is given as 0.72 square units.
Now you have 0.72 = 1/2 x S^2
First multiply both sides by 2:
1.44 = S^2
To find S, take the square root of both sides:
S = √1.44
S = 1.2
The side length is 1.2 units.