Question

express 5.09 ×10^-4 in standard form.

Answer 1

.000509.

when to is to a negative power move the decimal that many places to the left

Answer 2

It's in scientific notation >>>  5.09 × 10⁻⁴  <<<  

10^-4 negative number means: the decimal point has to move to the left, 4 decimal places. 

Result: 0.000509 (standard form)

I hope this helps! :)