# A right triangle has sides A, B, and C. Side A is the hypotenuse and side B is also a side of a rectangle. Sides A, C, and the side of the rectangle adjacent to side B have lengths of 4 , 1 , and 5 , respectively. What is the rectangle's area?

$A , B , C$ are the sides of a triangle, of which $A$ is the hypotenuse.
A=4 ; C=1 ; B= sqrt(A^2-C^2) = sqrt (4^2-1^2)=sqrt 15
$B = \sqrt{15}$, is one side of the rectangle and it's adacent side $D = 5$, is the other side of the rectangle.
Area of the rectangle is ${A}_{r} = B \cdot D = 5 \cdot \sqrt{15} = 19.36 \left(2 \mathrm{dp}\right)$sq.unit[Ans]