Question

The perimeters of the two rectangles at right are equal. Write and solve an equation to find the value of x and the common perimeter. (desperate need of help)

Answer 1

write the expression for the perimeter of the 1st rectangle 6x

write the expression for the perimeter of the 2nd rectangle 4x + 30

write the equation 6x = 4x + 30

x= 15

perimeter = 90

Explanation:

The perimeter is adding up all the sides of the rectangle.

So for the first one, we know two of the sides: x and 2x. The opposite sides have the same values. So the other two sides are x and 2x.

Therefore, the perimeter is

2x + x + 2x + x

or

6x

Similarly with the second rectangles:

(x+12) + (x+3) + (x+12) + (x+3)

Combine like terms

x + x + x + x + 12 + 3 + 12 + 3

4x + 30

Set these two equal to each other because the two perimeters are equal

6x = 4x + 30

Subtract 4x on both sides

2x = 30

Divide by 2 on both sides

x = 15

Check:

6(15) = 4(15) + 30

90 = 60 + 30

90 = 90

The common perimeter is

6*15 = 90 units