Finding the perimeter of a rectangle-Geometry Help

This video gives direction for finding the perimeter of a rectangle when only one side is given. The diagonal of a rectangle creates a right triangle that can be used to find the missing side.

Common Core Standard G-GPE.7

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Diagonal Length Rectangular Solid

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Video of the Day " Perimeter of a Rectangle"

Enjoy these two videos that cover finding the perimeter of a rectangle.

For more information please see: Perimeter of a rectangle

Top Ten Properties of a Rectangle

Top Ten Properties of a Rectangle

Rectangle

1. A rectangle is a quadrilateral so it has four sides.

2. A rectangle is a parallelogram

3. The perimeter of a rectangle equals 2(base X height)

4. The area of a rectangle equals base X height

5. Opposite sides of a rectangle are congruent

6. A rectangle has four right angles

7. The diagonal of a rectangle is the hypotenuse of a right triangle

8. Opposite sides of a rectangle are parallel

9. The diagonals of a rectangle do not intersect in a right angle.

10. The diagonals of a rectangle create opposite central angles that are congruent.

Area of a rectangle

Area of a rectangle

The formula for area of a rectangle is b*h (base times height)

In a rectangle the opposite sides are congruent so if you the measure of one side then you also know the measure of the opposite side.   

 Please watch the video to see each problem worked out

You Tube Area of a Rectangle

Here is a list of area formulas plane shapes

Problem 1. Find the area of a rectangle with a base of 10 units and a height of 8 units.

 

Step 1. Plug the numbers into the formula b*h 

 

8 * 10 =80 units squared

 

Next, let’s look at one more challenging. 

 

Problem 2. Find the base of a rectangle with an area of 100 units and a height of 5 units.

 

Step 1. Write the formula for the area of a rectangle Area= b*h

 

Step 2. Plug in what you know 100 = b * 5

 

Step 3 Divide each side by 5   100/5= b/5  

 

Step 4. 20 =b and b = the base of the rectangle

 

Problem 3. Find the area of a rectangle with a diagonal of 15 units and a side of 9 units.

 

Step 1. Plug in what you know A = b * 9

 

Step 2. The diagonal divides the rectangle into a right triangle. You can use the Pythagorean Theorem to find the base. 

A = 9 c= 15 b=your unknown (see picture below)

 

 

 

9^2+ b^2= 15^2 

81+ b^2=225

b^2=144  

b=√144 

b = 12

 

 

Step 3. Use your area formula of a rectangle Area = b*h

Area = 12 * 9 = 108 u^2