rectangle length 2X width, area equal to that of square w/ 12cm sides

anibal.antonio

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How can I solve this exercise or this type of exercise in general?

The length of a rectangle is twice it width and the area is equal to the area of a square with 12 cm sides. What will be the perimeter of the rectangle to the nearest whole number?
A. 51 cm
B. 36 cm
C.46 cm
D. 56 cm
 
How can I solve this exercise or this type of exercise in general?

The length of a rectangle is twice it width and the area is equal to the area of a square with 12 cm sides. What will be the perimeter of the rectangle to the nearest whole number?
A. 51 cm
B. 36 cm
C.46 cm
D. 56 cm

Let the algebra and notation help you.

One Important Rule: If you don't know its value, NAME IT, so you can talk about it.

L = Length of Rectangle
W= Width of Rectangle.

Immediately, you can start talking about these.
The AREA of the rectangle is L*W.
The PERIMETER of the rectangle is 2L + 2W.

We're told that the length is twice the width. Perfect: L = 2*W

Name it so you can talk about it. It's more than half the battle.
 
Alrighty, I did that, but at some moment when looking for the width using the area I have to look for the square root of a number in this case the number is 72, how can I find the square root of 72 without a calculator, or if there's another way of solving this exercise please tell me
 
Alrighty, I did that, but at some moment when looking for the width using the area I have to look for the square root of a number in this case the number is 72, how can I find the square root of 72 without a calculator, or if there's another way of solving this exercise please tell me
Is the use of a calculator forbidden in your class?
 
Alrighty, I did that, but at some moment when looking for the width using the area I have to look for the square root of a number in this case the number is 72, how can I find the square root of 72 without a calculator, or if there's another way of solving this exercise please tell me
Why do you need the square root of 72. Why just say sqrt(72) = 6sqrt(2)?

The area of the rectangle is 144cm2


So L*W = 2W*W =2W2 = 144 Then W2 = 72 and W = 6sqrt(2). Then L = 12sqrt(2)

edit: Oh, you have choices to choose from.
 
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How can I solve this exercise or this type of exercise in general?

The length of a rectangle is twice it width and the area is equal to the area of a square with 12 cm sides. What will be the perimeter of the rectangle to the nearest whole number?
A. 51 cm
B. 36 cm
C.46 cm
D. 56 cm

Clearly you do need a numerical value, not just a simplified radical.

If you are allowed to use a calculator, that is easy; if not, then one thing you can do is to use the simplified form, 6 sqrt(2), and the knowledge that sqrt(2) is about 1.414. That is enough to get the rounded value to sufficient accuracy.
 
I can't use a calculator, knowing the sqrt(2) helps that's the only way I could use that works and also I found that if I use the answers presented (a,b,c,d) I can solve the exercise like in reverse because I am given the area

Thank you guys, I appreciate your help
 
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