The motion of an pendulum can be modeled by the function

f(t) = 10cos(2t) * 0.95^t, where f is the horizontal displacement from the rest position, in centimeters, as a function of time, t, in seconds. What is the length of the pendulum?

I made two triangles, one with base 10 cm and another with base 8.48 because that is how far the pendulum travels when it returns. I couldn't figure out what to do from there. The answer in the back is 245 cm.