Answer:
A rectangle is quadrilateral with congruent and parallel opposite sides.
Mathematically, the area of a rectangle is
[tex]A_{rectangle}=b\times h[/tex]
Where [tex]b[/tex] is the base and [tex]h[/tex] is the height.
Now, the area of a triangle is defined as
[tex]A_{triangle} =\frac{b \times h}{2}[/tex]
Where [tex]b[/tex] is the base and [tex]h[/tex] is the height.
As you can notice, the are of a triangle is half of the area of a rectangle.
So, if we inscribe a triangle in a rectangle, we can find the area by doubling the triangle area.