The mass in a pendulum clock completes one complete swing in 1.00 s . what is the length of the rod?

The period of oscillation of a pendulum is

Where L is the length of the pendulum and the gravitational acceleration.
Re-arranging the formula and using T=1.0 s, we find the length of the pendulum:

This is the the concept of trigonometry, to get the sine value of the the function given we shall proceed as follows;
Using Pythagorean theorem, the hypotenuse of the triangle will be found as follows;
The side length will be 8 units since the y-coordinate is -8
The side width will be 3 units since the x- coordinate is 3  
c^2=a^2+b^2
c^2=(3)^2+(-8)^2
c^2=9+64
c^2=73
c=sqrt(73)

Therefore the sine value will be:
sin x=3/sqrt(73)
multiply both numerator and denominator by sqrt(73) we get:
sin x=(3√73)/73

Therefore the answer is A]