Brianna's teacher asks her which of these three expressions are equivalent to each other.



Expression A: 9x-3x-4

Expression B: 12x-4

Expression C: 5x+x-4



Brianna says that all three expressions are equivalent because the value of each one is - 4 when x=0.

Brianna's thinking is incorrect.



Identify the error in Brianna's thinking.

Determine which of the three expressions are equivalent.

Explain or show your process in determining which expressions are equivalent.



Enter your answers and your explanation or process in the box provided.

Briana's thinking is incorrect because the numbers are different when you substitute x with numbers other than 0.

the two equations that are equivalent to each other are,

5x+x-4 and 9x-3x-4

Step-by-step explanation:

Expression A: 9x-3x-4

Expression B: 12x-4

Expression C: 5x+x-4

First I will substitute x for each of the equations.

9x-3x-4

when x equals:, then y equals:

1 = 9 (1) - 3 (1) - 4 = 2

2 = 9 (2) - 3 (2) - 4=8

3 = 9 (3) - 3 (3) - 4 = 14

Now for 12x-4

when x equals:, then y equals:

1 = 12 (1) - 4 = 8

2 = 12 (2) - 4 = 20

3 = 12 (3) - 4 = 32

And for the final equation:

5x+x-4

when x equals:, then y equals:

1 = 5 (1) + (1) - 4 = 2

2 = 5 (2) + (2) - 4 = 8

3 = 5 (3) + (3) - 4=14

Based on this you can now see that the two equations that are equal are:

5x+x-4 and 9x-3x-4

~CaityConcerto

Expressions A and C are equivalent.

Step-by-step explanation:

Expression A: 9x-3x-4 Combine like terms 6x - 4

Expression B: 12x-4 There are no terms to combine 12x-4

Expression C: 5x+x-4 Combine like terms 6x - 4

Brianna only looked at one particular value for x. She must look at all values for x.