Final answer:
The input r(t) that creates the given steady-state output y(t) can be calculated by taking the inverse Laplace transform of the transfer function.
Step-by-step explanation:
To create the steady-state output y(t)=12cos(√3t-30°), the input r(t) can be found by rearranging the transfer function and equating it to the steady-state output. By comparing the given expression with the standard form of the transfer function, Hyr = K/(s+a)^2, we can see that K = 36 and a = 3. The input r(t) can be calculated by taking the inverse Laplace transform of the transfer function: r(t) = 36cos(√3t).