Classroom discussion

Misconceptions

Students' misconceptions

Subtract 4x - 5 from x^2 + 3x - 5

The biggest error students make is x^2 + 3x - 5 - 4x - 5 = x^2 - x -10

Teacher Prompts

Is this problem solved correctly?
How is this problem incorrect?
Why do you think many students make this error?
How can you explain or reinforce the use or parenthesis?
Is there a way to check your work when you think you've solved it?
Is there another way?
Can someone rephrase what he/she just said?
Will you elaborate on your explanation?

Correct

x^2 + 3x - 5 - (4x - 5) = x^2 + 3x - 5 - 4x + 5 = x^2 - x

This is an error students do though they technically know the parenthesis should be there, but they don’t put them in and promptly forget that they were there and do the subtraction incorrectly.