Express 0.00289 in standard form.

The standard form of a number is a way to express it using the format "a x 10^b " where $1\le a<10$ and b is an integer. This is also known as scientific notation. 

In this case, to express 0.00289 in standard form, we want to move the decimal point three places to the left to get 2.89, which is between 1 and 10, and the exponent will be -3 (indicating that we moved the decimal point 3 times to the left).

Therefore, 0.00289 = 2.89 x 10^-3.