Question

The work of a student to find the dimensions of a rectangle of area 8 + 16x and width 4 is shown below:

Step 1: 8 + 16x
Step 2: 4(4) + 4(12x)
Step 3: 4(4 + 12x)
Step 4: Dimensions of the rectangle are 4 and 4 + 12x

In which step did the student first make an error and what is the correct step?
Step 3; 4 + (4 + 12x)
Step 3; 4 + (4 ⋅ 12x)
Step 2; 4(2) + 4(4x)
Step 2; 4(2) + 4x(2)

Answer 1

@dan815

Answer 2

@DecentNabeel

Answer 3

To find the area of a rectangle what you do is:
length x width = area

You already have the width as 4 and area:
length x 4 = 8 + 16x
\[l \times 4 = 8 + 16x\]

To solve for l (length) you need to isolate and use the division property of equality:
\[\frac{ l \times 4 }{ 4 } = \frac{ 8 + 16x }{ 4 }\]

Clearly the student did the inverse in one of the steps. Can you find out which step he/she did that?

Answer 4

C Step 2; 4(2) + 4(4x)

Answer 5

Yes

Answer 6

Yay c:

Answer 7

Great job!

Answer 8

Thanks for your help (: