What is equivalent to 3 to the negative 2nd power

3 to the negative second power is written like this: . 

When simplifying an expression with a negative exponent, you take a positive version of the exponent, in this case that would be 2, and apply that to the base. 
After doing that, we have 9. 
The next step is to put one over that number.
In this case, now after doing that the answer is . 

Hope this helps!