Question

find the third proportional to 9 and 12

Answer 1

Let the third proportion to 9 & 12 be 'x'.

=> 9:12 = 12 :p

=> p = 12x12/9 = 16.

Answer 2

Let the third proportional to 9 and 12 be x.

Then the fourth propotionalto 9,12,12 is x.

therefore,9:12::12:x

9*x=12*12

x=(12*12)/9=16