Solve for Rectangle Dimensions: Area = 12 cm² and Perimeter = 14 cm

Question

The perimeter of a rectangle is 14 cm.

The area of the rectangle is 12 cm².

What are the lengths of its sides?

Video Solution

Solution Steps

00:00 Find the sides of the rectangle
00:03 Let's draw the rectangle
00:06 Mark the sides with X and Y
00:12 The perimeter of the rectangle equals the sum of its sides
00:18 Let's substitute the perimeter value and solve for the sum of sides
00:26 This is the sum of the sides
00:29 Now let's use the formula to calculate the rectangle's area (side multiplied by side)
00:33 Let's express X in terms of Y
00:43 Let's substitute our X and solve for Y
00:46 Open the parentheses properly - multiply each term
00:57 Arrange the equation so that the right side equals 0
01:06 Find the possible solutions for Y
01:10 These are the possible solutions for Y
01:17 Now let's substitute them to find X
01:28 We can see these are the options for our sides
01:36 And this is the solution to the problem

Step-by-Step Solution

Since in a rectangle each pair of opposite sides are equal to each other, let's call each pair of sides X and Y

Now let's set up a formula to calculate the perimeter of the rectangle:

2x+2y=14 2x+2y=14

Let's divide both sides by 2:

x+y=7 x+y=7

From this formula, we'll calculate X:

x=7y x=7-y

We know that the area of the rectangle equals length times width:

x×y=12 x\times y=12

We know that X equals 7 minus Y, let's substitute this in the formula:

(7y)×y=12 (7-y)\times y=12

7yy2=12 7y-y^2=12

y27y+12=0 y^2-7y+12=0

(y3)×(y4)=0 (y-3)\times(y-4)=0

From this we can claim that:

y=3,y=4 y=3,y=4

Let's go back to the formula we found earlier:

x=7y x=7-y

Let's substitute y equals 3 and we get:

x=73=4 x=7-3=4

Now let's substitute y equals 4 and we get:

x=74=3 x=7-4=3

Therefore, the lengths of the rectangle's sides are 4 and 3

Answer

3, 4