Question

As students move to thinking about formulas it supports their conceptual knowledge of how the perimeter of rectangles can be put into general form. What formula below displays a common student error for finding the perimeter?

A) P = l + w + l + w
B) P = l + w
C) P = 2l + 2w
D) P = 2(l + w)

Answer 1

B.
`P=l+w`

Explanation:

Let l represent length of rectangle and w represent width of rectangle.

We have been given four formulas for the perimeter of rectangle. We are asked to choose the formula that displays a common student error for finding the perimeter.

We know that perimeter of a polygon is sum of all sides of the polygon. We also know that rectangle is polygon having two sets of equal sides.

The perimeter, P, of rectangle will be sum of its all sides that is:

`P=l+w+l+w`

Combine like terms:

`P=2l+2w`

Factor out 2:

`P=2(l+w)`

Upon looking at our given choices, we can see that formula represented by option B displays a common student error for finding the perimeter.