How to find the area of a half circle with a diameter of 22?

Question

its not my homework but im trying to figure out whats written on my book. i dont get it. tnx.

Answer 1

A = (1/2) π r ²

A = (1/2) π (11 ²)

A = 190.1 units ² ( to 1 dec. place )

Answer 2

The formula for the area of a circle is:

      A = pi * r^2    

where r is the radius and is related to the diameter by r=d/2

So, if we plug in 22 for 'd', we get r = 11.  We then stick this into the formula for the area and get:

       A = pi * 11^2 = pi * 121

Now we have the area of a circle with diameter 22.  To find the area of the corresponding half circle, we just divide by 2:  

      A = (pi*121)/2

If you are interested in where the formula A = pi*r^2 comes from, visit:

http://www.worsleyschool.net/science/fil...

There is a short, good, and uncomplicated explanation.

Answer 3

I don't recall the perimeter/area equations, but find the area of a whole circle (diameter of 22) and divide your answer by 2.

Answer 4

Area = pi x r^2

= 3.14159 x (22/2)^2

= 3.14159 x 11^2

= 3.14159 x 121

= 380.13

Half circle = Area/2, or 380.13 / 2  = 190.07

Answer 5

([pi]D) / 2

The whole [pi] thing is the 3.14 thing, you know? D = diameter, which, in this case, is 22. And then divide it all by 2, because [pi]D is the area of a full circle.