The formula T=2*pi*sqrt[L/g] gives the period of a pendulum of length l feet. The period P is the number of seconds it takes for the pendulum to swing back and forth once. Suppose we want a pendulum to complete three periods in 2 seconds. How long should the pendulum be?

Answer 1

Solve for L in:
2=2π√(L/g)
π²L/g=1
L=g/π²

Substitute this expression into the formula to see if you do get T=2.