19. The period (the time required to complete one swing) of a simple pendulum varies directly as the square root of
its length. If a pendulum 12 feet long has a period of 4
seconds, find the period of a pendulum 3 feet long.

go on the tube you might find some information there

or

step-by-step explanation:

we need to solve for 'x' the following equation:  

we have that:

⇒

⇒ ⇒

factorizing, we get that:

  ⇒

then, the solutions are: or

nothing extraneous has been found!

answer: not good

step-by-step explanation:

multiply by the conjugate

the conjugate is the bottom express (6-√13) with the middle changed to +

or (6+√13)

so times it be   (6+√13)/(6+√13)