Final answer:
The function that is a solution to (d²y/dx²) = -9²y is y = sin(9x).
Step-by-step explanation:
The function that is a solution to (d²y/dx²) = -9²y is B. y = sin(9x).
To check this, we can take the second derivative of y = sin(9x) and substitute it into the given equation:
d²y/dx² = (9² * -sin(9x)) = -9² * sin(9x)
Now we can compare this with the right side of the equation, which is -9²y:
-9² * sin(9x) = -81 * sin(9x), which is the same as -9²y
Therefore, the function y = sin(9x) is indeed a solution to the given equation.