Answer:
Step-by-step explanation:
The product of the lengths of the parts of the chord is equal to the product of the lengths of the parts of the chord that divides it.
(7 cm)*(8 cm) = n*(4 cm)
(7*8 cm²)/(4 cm) = n
14 cm = n

u take ur known variables and fill them in, pi will be filled in as 3.14
Example:

Then divide both sides by 3.14, after that it should be (number) =r². since it's squared you have to find to square root of both.
Example:

therefore in this example the radius is 7