188k views
4 votes
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.

User Jane Doh
by
7.4k points

1 Answer

6 votes
The error in Brianna's thinking is that she only tested the expressions when x is equal to 0. However, to determine if the expressions are equivalent, we need to test them for all possible values of x.

Expression A: 9x - 3x - 4 = 6x - 4
Expression B: 12x - 4
Expression C: 5x + x - 4 = 6x - 4

Expressions A and C are equivalent because they both simplify to 6x - 4. Expression B is not equivalent to either of the other expressions because it cannot be simplified any further.

Hope this helps
User SoCo
by
8.1k points