Question

If the third proportional to 9 and x is 28 find the value of x

Answer 1

The third proportional of two numbers a and b is defined to be that number c such that a : b = b : c. So you want to find a number c such that 12 : 18 = 18 : c. That number is 27. If BD = AC, then the 3rd proportional to AB and AC is CE.

Answer 2

Heya!  

here's your answer -

Third proportional 'c' = a:b::b:c

Then, 9 : x :: x : 28

So, 9/x = x/28

x² = 9 × 28  

x = √9 × 28

x = √252

x = 15.875

Hope it helps!