Answer:

This is approximately equal to 18.76166 units.
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Step-by-step explanation
A rhombus has all four sides the same length.
The perimeter is 52 units, so each side of the rhombus is 52/4 = 13 units long.
I'm assuming you meant to say AC = 18. If so, then the diagonals of the rhombus bisect each other at point E, which lead to AE = 9 and EC = 9.
Focus on one of the smaller right triangles. Let's say we focus on right triangle AEB.
The known leg is AE = 9. The unknown leg EB is x. Hypotenuse AB is 13 units long.
Use the Pythagorean theorem
and it leads to the equation
. Skipping a bit of steps, that equation solves to

Therefore

Side note:
