To write 721,000 in scientific notation:

1. Move the decimal point so the number is between 1 and 10.

   • The decimal point in 721,000 is originally after the last zero: $721,000.0$.
   • Move the decimal 5 places to the left: $7.21$.

2. Multiply by $10$ raised to the number of places moved.

   • Since we moved 5 places, the power of 10 is 5.

Thus, the scientific notation for 721,000 is:
$\mathbf{7.21 \times 10^5}$

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Related Questions:

1. How do you write 0.00054 in scientific notation?
2. What is $5.6 \times 10^4$ in standard form?
3. How do you determine the exponent in scientific notation?
4. Write $123,400,000$ in scientific notation.
5. Convert $8.3 \times 10^{-3}$ to standard form.

Tip: When writing numbers in scientific notation, always ensure the first part (the coefficient) is between 1 and 10.