Replace ? with an expression that will make the equation valid. \[ \frac{d}{d x} \ln \left(x^{6}+7\right)=\frac{1}{x^{6}+7} ? \] The missing expression is

Step 1 ：Let the function inside the natural logarithm be u, where u = x^6 + 7.

Step 2 ：The derivative of u with respect to x, du/dx, is 6x^5.

Step 3 ：The derivative of the natural logarithm function, ln(u), where u is a function of x, is given by the chain rule as 1/u * du/dx.

Step 4 ：Substituting the values of u and du/dx, we get 1/(x^6 + 7) * 6x^5.

Step 5 ：Therefore, the missing expression in the equation is 6x^5.

Step 6 ：Final Answer: The missing expression is \(\boxed{6x^{5}}\).