Here's how to convert it:

1. Move the decimal point to the right until you have a number between 1 and 10. In this case, we need to move it 5 places to the right: 9.21

2. Count the number of places you moved the decimal. Since we moved it 5 places to the right, the exponent will be -5.

3. Write the number in the form a x 10^b, where 'a' is the number between 1 and 10 and 'b' is the exponent.

Therefore, 0.0000921 is equal to 9.21 x 10^-5.