# Trapezoid - Regular or Isosceles

 Definition: A regular trapezoid is a trapezoid whose non-parallel sides are congruent (of equal length). Interactivity 1: Regular trapezoid    Directions for interactivity Click and drag the slider buttons to change the size. Click and drag point B to move and point А to rotate. This browser does not have a Java Plug-in. Get the latest Java Plug-in here.
Basic formulas for a regular trapezoid with base a , top b и height h are:
• area: A=\,\frac{a+b}{2} \, h (same as for any trapezoid)
• c=\sqrt{ \left( \frac{a-b}{2} \right)^2+h^2} length of the non-parallel sides c (using Pythagoras') , a h=\sqrt{ c^2-\left( \frac{a-b}{2} \right)^2}
• perimeter: L=a+b+2c

Examples for the area and perimeter of a regular trapezoid.

Check the following examples using the above interactivity.

Dimensions of the trapezoid: Area Side Perimeter
a b h A=\frac{a+b}{2} \, h c=\sqrt{ \left( \frac{a-b}{2} \right)^2+h^2} L=a+b+2c
10 \,cm 4 \,cm 2 \,cm \frac{10+4}{2} \,cm \cdot 3 \,cm=14 \,cm^2 c=\sqrt{ \left( \frac{10-4}{2} \right)^2+2^2} \,= 3,6 \,cm L=21,2 \,cm
8 \,mm 5 \,mm 2 \,mm \frac{8+5}{2} \,mm \cdot 2 \,mm=13 \,mm^2 c=\sqrt{ \left( \frac{8-5}{2} \right)^2+2^2} \,= 2,5 \,mm L= 18 \,mm
0,09 \,m 8 \,cm 30 \,mm \frac{9+8}{2} \,cm \cdot 3 \,cm=25,5 \,cm^2 c=\sqrt{ \left( \frac{9-8}{2} \right)^2+3^2} \,= 3 \,cm L= 23,1 \,cm

Interactivity 2: Construct a regular trapezoid

 1. Examine the regular trapezoid in the above interactivity.. 2. Now construct a regular trapezoid with the same properties. If you need help with the steps, click here to open a new window with directions?. Check whether your construction is stable - Is your construction always a regular trapezoid no matter what slider or point you move? This browser does not have a Java Plug-in. Get the latest Java Plug-in here.
 Rules The diagonals of a regular trapezoid are congruent (same length). Click and drag points A and B. This browser does not have a Java Plug-in. Get the latest Java Plug-in here. Notice the difference between these and the rules of trapezoids! A regular trapezoid is determined by the lengths of its base, top and height. A regular trapezoid is determined by the lengths of its base, top and side.

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