In the “Operations with Expressions”, Greg mentioned about x isn’t = to 0. Did he mean “x isn’t = to 0” for the **blue** marked equation or the **red** marked one?

Can anyone help me with this confusion?

Both.

- x cannot be 0 for the blue one because if you do so, you get a 0/0 case which isn’t valid.
- x cannot be 0 for the red one because by dropping x from the denominator in the previous step, you are implicitly assuming that x isn’t 0 (otherwise, you may end up thinking that x is only not equal to -4/5, which isn’t correct)

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