Question

Find the mean proportional of the following:

9, 25

Answer 1

Let x be the mean proportional between 9 and 25.

Then,

9 : x :: x : 25

⇒ 9 : x = x : 25

⇒ `9/x = x/25`

⇒ x × x = 9 × 25

⇒ x² = 225

⇒ x = `sqrt225`

⇒ x = 15