# The number obtained on rationalising the denominator of 1/(√7 - 2) is

a. (√7 + 2)/3

b. (√7 - 2)/3

c. (√7 + 2)/5

d. (√7 + 2)/45

**Solution:**

Given

1/(√7 - 2)

Let us multiply both __numerator__ and __denominator__ by √7 + 2

= 1/(√7 - 2) x (√7 + 2)/(√7 + 2)

Using the __algebraic identity__ (a + b) (a - b) = a² - b²

= (√7 + 2)/ (7 - 4)

By further calculation

= (√7 + 2)/ 3

Therefore, the number obtained is (√7 + 2)/ 3.

**✦ Try This: **The number obtained on rationalising the denominator of 1/(√5 - 2) is

Given

1/(√5 - 2)

Let us multiply both numerator and denominator by √5 + 2

= 1/(√5 - 2) x (√5 + 2)/(√5 + 2)

Using the algebraic identity (a + b) (a - b) = a² - b²

= (√5 + 2)/ (5 - 4)

By further calculation

= (√5 + 2)/ 1

Therefore, the number obtained is (√5 + 2).

**☛ Also Check: **NCERT Solutions for Class 9 Maths Chapter 1

**NCERT Exemplar Class 9 Maths Exercise 1.1 Problem 12**

## The number obtained on rationalising the denominator of 1/(√7 - 2) is a. (√7 + 2)/3, b. (√7 - 2)/3, c. (√7 + 2)/5, d. (√7 + 2)/45

**Summary**:

The number obtained on rationalising the denominator of 1/(√7 - 2) is (√7 + 2)/ 3

**☛ Related Questions:**

visual curriculum