Get the calculator out. We can use calculators for this part of the AP exam. I assume they intend us to because this isn't something that's easy to calculate by hand. The acceleration at time 5.5, we just have to say t is 5.5 and evaluate this function. 1 half, I'll just write.5 times e to the t over 4. t is 5.5. 5.5 divided by 4 and then times cosine of 5.5 divided by 4. Gives us.38.