Areas and Perimeters?

• May 30th 2009, 11:38 PM
suckatmaths
I did these problems, teacher said they were wrong and sent me away to do them again. I tried and still got the same answers. :(
*

A) Find the perimeter to the figure
B) The Enclosed area:

Picture:

12002.jpg picture by EdenJonas - Photobucket

Thanks
• May 31st 2009, 12:20 AM
Moo
Hello,
Quote:

Originally Posted by suckatmaths
I did these problems, teacher said they were wrong and sent me away to do them again. I tried and still got the same answers. :(
*

A) Find the perimeter to the figure
B) The Enclosed area:

Picture:

12002.jpg picture by EdenJonas - Photobucket

Thanks.

Please provide the results (and the working) you got. It would be easier to see where the mistakes are, if there are any. What do you find ? I have the answers...
• May 31st 2009, 01:25 AM
suckatmaths
A) 10squared + 8squared=
100+64
=164
=squareroot164 = 12.80

10+8+12.80 = 30.8cm.

(see? I suck)

B) 1/2 12.80x8

6.4x8
=51.2

There is just this major question mark next to them.
• May 31st 2009, 01:39 AM
Moo
Quote:

Originally Posted by suckatmaths
A) 10squared + 8squared=
100+64
=164
=squareroot164 = 12.80

10+8+12.80 = 30.8cm.

(see? I suck)

B) 1/2 12.80x8

6.4x8
=51.2

There is just this major question mark next to them.

Okay, your mistake comes from the application of the Pythagorean theorem.

In a right angle triangle, the hypotenuse is the longest side. It is also the side opposit to the right angle. So here, the hypotenuse is the side which length is 10.
And the Pythagorean theorem says $(\text{Hypotenuse})^2=(\text{Side}_1)^2+(\text{Sid e}_2)^2$

Hence the length of the third side is not $10^2+8^2$, but... ?
• May 31st 2009, 01:43 AM
suckatmaths
6squared? :\
I'm sorry, I am really bad at this.

Oh wait, is it = 10squared = 8squared + 6squared?
• May 31st 2009, 01:51 AM
Moo
Quote:

Originally Posted by suckatmaths
6squared? :\
I'm sorry, I am really bad at this.

Oh wait, is it = 10squared = 8squared + 6squared?

Yes (Nod)

So the length of the third side is 6 ! (not 6squared... read carefully the formula from the Pythagorean theorem)
• May 31st 2009, 01:54 AM
suckatmaths
So therefore do I just:

10squared + 8squared + 6squared = perimeter?

Then squareroot = perimeter?
• May 31st 2009, 02:00 AM
Moo
Quote:

Originally Posted by suckatmaths
So therefore do I just:

10squared + 8squared + 6squared = perimeter?

Then squareroot = perimeter?

Okay... It looks like you have big problems with basics (Doh)

The perimeter is the sum of the sides that are on the outside.
This means that the perimeter of your figure is 8+10+the length of the semicircle.
You're not asked for the perimeter of the triangle !!!

Now, do you know the formula for the perimeter and the area of a circle ?
What is the radius of this semicircle ?

The perimeter of the triangle would be 8+10+6.
Not with the squares. Please read carefully the formula from the Pythagorean theorem !
• May 31st 2009, 02:04 AM
suckatmaths
Radius of the semicircle is 3.

Do I go: 3*pi = 9.42m

Then add: 9.42 + 10 + 8

The perimeter = 27.42m?
• May 31st 2009, 02:05 AM
Moo
Quote:

Originally Posted by suckatmaths
Radius of the semicircle is 3.

Do I go: 3*pi = 9.42m

Then add: 9.42 + 10 + 8

The perimeter = 27.42m?

Exactly ! (Clapping)

But did you understand the path to come up with this solution ?
• May 31st 2009, 02:06 AM
suckatmaths
Yay, it only took me forever. Ahahaha.
Thank you for all your help on that one. :)

Quote:

Originally Posted by Moo
Exactly ! (Clapping)

But did you understand the path to come up with this solution ?

Yes, I finally got there. I have to READ the question, and work out everything... The perimeter of not JUST the triangle, but the circle aswell.
So thank you. :)