Maharashtra Board Solutions Class 9-Maths (Part 1): Chapter 2.2- Real Numbers

Class 9: Maths Chapter 2.2 solutions. Complete Class 9 Maths Chapter 2.2 Notes.

Maharashtra Board Solutions Class 9-Maths (Part 1): Chapter 2.2- Real Numbers

Maharashtra Board 9th Maths Chapter 2.2, Class 9 Maths Chapter 2.2 solutions

Question 1.
Show that 4√2 is an irrational number.
Solution:
Let us assume that 4√2 is a rational number .
So, we can find co-prime integers ‘a’ and ‘b’ (b ≠ 0) such that
4√2 = ab
∴ √2 = a4b
Since, a and b are integers, a4b is a rational number and so √2 is a rational number.

Alternate Proof:
Let us assume that 4√2 is a rational number.
So, we can find co-prime integers ‘a’ and ‘b’ (b ≠ 0) such that

Since, 32 divides a², so 32 divides ‘a’ as well.
So, we write a = 32c, where c is an integer.
∴ a² = (32c)² … [Squaring both the sides]
∴ 32b² = 32 x 32c² …[From(i)]
∴ b² = 32c²
∴ c² = b232
Since, 32 divides b², so 32 divides ‘b’.
∴ 32 divides both a and b.
a and b have at least 32 as a common factor.
But this contradicts the fact that a and b have no common factor other than 1.
∴ Our assumption that 4√2 is a rational number is wrong.
∴ 4√2 is an irrational number.

Question 2.
Prove that 3 + √5 is an irrational number.
Solution:
Let us assume that 3 + √5 is a rational number.
So, we can find co-prime integers ‘a’ and ‘b’ (b ≠ 0) such that

Since, a and b are integers, ab – 3 is a rational
number and so √5 is a rational number.
But this contradicts the fact that √5 is an irrational number.
∴ Our assumption that 3 – √5 is a rational number is wrong.
3 + √5 is an irrational number.

Question 3.
Represent the numbers √5 and √10 on a number line.
Solution:
i. Draw a number line and take point A at 2.
Draw AB perpendicular to the number line such that AB = 1 unit.
In ∆OAB, m∠OAB = 90°
∴ (OB)² = (OA)² + (AB)² … [Pythagoras theorem]
= (2)² + (1)²
∴ (OB)² = 5
∴ OB = √5 units. … [Taking square root of both sides]
With O as centre and radius equal to OB, draw an arc to intersect the number line at C.

The coordinate of the point C is √5 .

ii. Draw a number line and take point Pat 3.
Draw PR perpendicular to the number line such that PR = 1 unit.
In ∆OPR, m∠OPR = 90°
∴ (OR)² = (OP)² + (PR)² … [Pythagoras theorem]
= (3)² + (1)²
∴ (OR)² = 10
∴ OR= √10units. … [Taking square root of both sides]
With O as centre and radius equal to OR, draw an arc to intersect the number line at Q.

The coordinate of the point Q is √10 .

Question 4.
Write any three rational numbers between the two numbers given below.
i. 0.3 and – 0.5
ii. – 2.3 and – 2.33
iii. 5.2 and 5.3
iv. – 4.5 and – 4.6
Solution:
i. 0.3 = 0.30 and -0.5 = -0.50
We know that,
0. 30 >0.29 >….. >0.10>.. > – 0.10>…. > -0.30>…> -0.50
∴ the three rational numbers between 0.3 and -0.5 are -0.3, -0.1 and 0.1.

Alternate Method:
A rational number between two rational numbers a and b


∴ the three rational numbers between 0.3 and -0.5 are -0.3, -0.1 and 0.1.

ii. -2.3 = -2.300 and -2.33 = -2.330
We know that,
-2.300 > -2.301>… > -2.310>…> -2.320>…> -2.330
∴ the three rational numbers between -2.3 and -2.33 are -2.310, -2.320 and -2.325.

iii. 5.2 = 5.20 and 5.3 = 5.30
We know that,
5.20 < 5.21 < 5.22 < 5.23 < … < 5.30
∴ the three rational numbers between 5.2 and 5.3 are 5.21, 5.22 and 5.23.

iv. -4.5 = -4.50 and -4.6 = -4.60 We know that,
-4.50 > -4.51 > -4.52 >… > – 4.55 >…>- 4.60
∴ the three rational numbers between -4.5 and -4.6 are -4.51, -4.52 and -4.55.

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Maharashtra Board Solutions Class 9-Maths (Part 1): Chapter 2.2- Real Numbers

Download PDF: Maharashtra Board Solutions Class 9-Maths (Part 1): Chapter 2.2- Real Numbers PDF

Chapterwise Maharashtra Board Solutions Class 9 Maths :

Part 1

• Chapter 1.1- Sets
• Chapter 1.2- Sets
• Chapter 1.3- Sets
• Chapter 1.4- Sets
• Chapter 2.1- Real Numbers
• Chapter 2.2- Real Numbers
• Chapter 2.3- Real Numbers
• Chapter 2.4- Real Numbers
• Chapter 2.5- Real Numbers
• Chapter 3.1- Polynomials
• Chapter 3.2- Polynomials
• Chapter 3.3- Polynomials
• Chapter 3.4- Polynomials
• Chapter 3.5- Polynomials
• Chapter 3.6- Polynomials
• Chapter 4.1- Ratio and Proportion
• Chapter 4.2- Ratio and Proportion
• Chapter 4.3- Ratio and Proportion
• Chapter 4.4- Ratio and Proportion
• Chapter 4.5- Ratio and Proportion
• Chapter 5.1- Linear Equations in Two Variables
• Chapter 5.2- Linear Equations in Two Variables
• Chapter 6.1- Financial Planning
• Chapter 6.2- Financial Planning
• Chapter 7.1- Statistics
• Chapter 7.2- Statistics
• Chapter 7.3- Statistics
• Chapter 7.4- Statistics
• Chapter 7.5- Statistics