To solve the problem in the image, we need to calculate the value of $\sum a^2$ given the values for $x$. The sum notation suggests that we need to sum the squares of the given values of $x$.

The given values of $x$ are: $x = 3, \ 5, \ 9$

To calculate $\sum a^2$, we square each of these values and then sum them:

$3^2 = 9$ $5^2 = 25$ $9^2 = 81$

Now, sum these squares:

$\sum a^2 = 9 + 25 + 81 = 115$

So, the value of $\sum a^2$ is 115.

Would you like more details or have any questions?

Here are some related questions you might find useful:

1. What is the general formula for calculating $\sum a^2$ given a set of values?
2. How does the sum of squares relate to the standard deviation?
3. What would $\sum (a + b)^2$ look like for a given set of values $a$ and $b$?
4. Can you explain how to calculate the mean of these squared values?
5. How is $\sum a^2$ used in statistical analyses like variance?

Tip: The sum of squares is a fundamental concept in statistics and is used to measure the spread or variability of a set of data points.