This is an important ques from the Book ML Aggarwal class 10th,, chapter – 7, ratio and proportion.
In this question we have been given three numbers with a fixed constant x, and they are in mean proportion and we have to find the value of x.
Question 9, exercise 7.2
Solution:
It is given that
x + 5 is the mean proportion between x + 2 and x + 9
We can write it as
(x + 5)2 = (x + 2) (x + 9)
By further calculation
x2 + 10x + 25 = x2 + 11x + 18
x2 + 10x – x2 – 11x = 18 – 25
So we get
– x = – 7
x = 7