Geometry: Getting Started - Area of Polygons and Circles
This is a free lesson from our course in Geometry 
 
   
Parallelogram
It is a quadrilateral with two pairs of parallel sides.
Properties and important points to remember-
• Opposite sides of a parallelogram are equal in length.
• Opposite angles of a parallelogram are equal in measure.
(More text below video...)
<h2> Getting Started - Areas of Polygons and Circles - Watch video (Geometry)</h2> <p> area, measure, square, formula, video, area of polygons and circles, solution, geometry, square unit, example, practice questions</p> <p> If we are given the base of the triangle (b) and the perpendicular height (h); to calculate area use the formula: 1/2 x base x height</p>
Other useful lessons:
Area of a Rectangle
Area of a Triangle - Areas of Polygons and Circles
Area of a Square
Area of a Parallelogram
Area of a Trapezoid
Area of a Circle
Effect of dimension changes on Area
Real World Applications - Area of Polygons and Circles
(Continued from above) • Opposite sides of a parallelogram can never intersect.
• The diagonals of a parallelogram bisect each other.
• Consecutive angles are supplementary, add to 180°.
• Area (A), of a parallelogram is A = bh, where is the base and is height of parallelogram.
• The area of a parallelogram is twice the area of a triangle created by one of its diagonals. “A parallelogram is a quadrilateral with opposite sides parallel and congruent”.

Notice that:
• A rectangle is a parallelogram, but with each angle as 90°.
• A rhombus is a parallelogram, but with all sides equal in length.
• A square is a parallelogram but with all sides equal in length, and each angle at 90°
Example 2: Given- the figure below shows the dimensions of side and diagonal of the parallelogram ABCD. The measure of angles A and C are each 45°. Find out the area of ABCD.
Study and analyze the given information carefully.
Step 1: ABCD is a parallelogram, as both the opposite sides are equal. AB = CD and AD = BC.
Step 2: Use the formula A = length * height. Now calculate the length and height.
Step 3: AD2 = (52)2 + (52)2 = 100.
Thus AD = 10 (taking sq root on both sides).
Step 4: Drop the perpendicular from B, which will create 45°, 45°, and 90° triangle. The hypotenuse of that triangle will be AB.
Step 5: You know that sides of this special triangle shall be in the ratio of 1:1:2. From this height of this triangle will be 5.
Step 5: Area thus equals = 5 * 10 =50 units, as the final answer.
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