Question

find the mean propotional between 8and 18

Answer 1

Let the mean proportional between 8 and 18 be x
Therefore 
8:x = 18:x
x² = 8*18
x = √144 = 12
12 is the answer.

Answer 2

let the mean proportional be x

so

8:x = x : 18

x^2 = 18 x 8

x^2 = 144

x = 12

hence 12 is the mean proportional between 8 and 18