After you expand $(x+7)^2$, carefully subtract $49$ and combine like terms. You should end up with a simpler polynomial in standard form.

Once you have the simplified polynomial, check if all terms share a common factor that you can factor out.

In Desmos, enter the original expression as y1 = (x + 7)^2 - 49 to create its graph.

For each answer choice, type its expression as y2, y3, etc. For example, take the expression from option A and type it exactly after y2 =, then do the same with options B, C, and D as separate functions.

Look at the graphs of y1 and each of the other functions. The choice that is equivalent will have a graph that lies exactly on top of y1 for all values of $x$ (the two graphs are the same curve everywhere). That option is the equivalent expression.

Use the formula for squaring a sum: $(a+b)^2 = a^2 + 2ab + b^2$.

Here, $a=x$ and $b=7$:

So the expression becomes

Now simplify by combining the constant terms $+49$ and $-49$:

So the original expression simplifies to $x^2 + 14x$.

Factor $x^2 + 14x$ by taking out the greatest common factor, which is $x$:

Therefore, $(x+7)^2 - 49$ is equivalent to $x(x + 14)$.