how do we write .00000678 in scientific notation?

would this be 6.78*10^-6

Yes.

7x+3-2x

To write the number $0.00000678$ in scientific notation, you need to express it as a number between $1$ and $10$ multiplied by a power of $10$. Here's how you can do it:

1. Start by counting the number of decimal places between the first non-zero digit and the decimal point. In this case, there are six decimal places.

2. Move the decimal point to the right of the first non-zero digit, which gives you $6.78$.

3. Rewrite this number as $6.78 \times 10^{-6}$, where $10^{-6}$ represents moving the decimal point six places to the left.

So, yes, you are correct! The number $0.00000678$ in scientific notation is $6.78 \times 10^{-6}$.