00:01
Okay, so let's start by defining this.
00:02
The circumference is the distance around the circle.
00:17
Now, area is the flat surface that it covers.
00:31
So if you're looking at a circle, the circumference, this is the circumference.
00:39
That's the circumference.
00:41
The area is all the inside.
00:48
Okay.
00:49
So a sprinkler waters the circle in a circular pattern.
00:53
It sprays water out of distance of 20 feet to the nearest foot.
00:57
How much long surface does the sprinkler cover? so this is the sprinkler and it's spraying out 20 foot and it's going all the way around the circle.
01:08
It's spraying everything inside of that.
01:11
It's not just spraying around.
01:12
So this is an area problem.
01:15
So you would do that sprays out 20 foot.
01:19
That's your radius.
01:21
So area equals pi times the radius squared.
01:24
So you would do 3 .14 for pi because it tells you here times 20 squared.
01:43
So that's 1 ,256 square foot.
01:51
I'm going to skip on over to number 7 because it's right what is the area of the shaded region? well, of course, you're using the area.
02:02
Well, we've got to find the area of the inside first.
02:06
So the area of the inside is five squared times pi, which is 25 pi.
02:14
I'll finish it out in a second.
02:16
The area of the outside ring is six squared pie, which is 36 pi.
02:23
So 25 times 3 .14 is 78 .5 square meters.
02:36
36 times 3 .14 is 113 .04 square meters.
02:44
Now i've got to subtract.
02:46
So i'm going to do 113 .04 minus the 78 .5.
02:51
That gives me 34 .34.
02:56
That gives me 34 .34 .3 .34 .4.
02:57
That gives me 34 .3 .3 .3.
02:57
4 .54 square meters.
03:07
Number two, a round swimming pool has a radius of 8 foot.
03:12
So i've got a round swimming pool with a radius of 8 foot.
03:16
To the nearest foot, what is the pool circumference? well, you're going to use the circumference because it tells you.
03:22
So this is 8.
03:23
So that's circumference equals 2 times pi times the radius.
03:28
So 2 times 5, which is 16 pi, which equals 16 times 3 .14 is 50 .24 feet.
03:45
To the nearest square meter, what is the area? okay, so now that's telling me the area.
03:52
I know to use area formula of a circular rose garden that has a radius of five meters...