Is this the correct formula:
( = pi*r^2) or this one A=1/2*pi*r^2

@jim_thompson5910
@ganeshie8

Question

Is this the correct formula:
 ( = pi*r^2)  or this one   A=1/2*pi*r^2

@jim_thompson5910 
@ganeshie8

vishweshshrimali5 · Answer

1/2*pi*r^2

anonymous · Answer

With the first equation I got 40 , 
with the 2nd equation I got 20.

jim_thompson5910 · Answer

How did you get 40?

anonymous · Answer

Check the question title, that's why I'm asking which equation is correct...

jim_thompson5910 · Answer

What's the diameter of this semi-circle?

anonymous · Answer

I already did all that :
The two radius' are  5  and  3.5  . 

I just don't know which formula is correct!

If the 1st formula in the title is correct than the answer would be 40,
if the 2nd formula in the title is correct than the answer would be  20 instead.

jim_thompson5910 · Answer

A = pi*r^2 is the area of a whole circle

A = 1/2*pi*r^2 is the area of half a circle

anonymous · Answer

Ah! That's why..
-------------
I solved it  these two ways:
1st equation

$$A  =\pi*5^2$$
$$A= 78.539 \approx 78.54 $$  

$$A  =\pi*3.5^2$$
$$A= 38.48  $$  

$$78.53-38.48=40.05$$

jim_thompson5910 · Answer

ok now you can cut that answer in half since you only want the upper half (not the entire circle)

anonymous · Answer

Now, if you use the second equation it would imply the answer is 20 .

jim_thompson5910 · Answer

good

anonymous · Answer

:D Yay.