First you need to find at least two dimensions of the triangle containing a side length of x. The triangle of the top can be used for that. The hypothenuse for the 7,3 triangle is .
Now we can use the other triangle with sides of x,, and a hypothenuse of 9 to find x.
x^2 + = 9^2
simplify
x^2 + 58 = 81
subtract 58 from both sides
x^2 = 23
x =
and since this radical cannot be simplified further that is your answer.
The line of symmetry can be defined as the axis or imaginary line that passes through the center of the shape or object and divides it into identical halves.