Let's Recall Solutions | Lesson 5 Expansion Formulae | Class 8 Maths English Medium | Maharashtra Board

 

Let's Recall – Lesson 5 Expansion Formulae

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In this post, you will find the complete Let's Recall solutions of Lesson 5 – Expansion Formulae for Class 8 Maths (English Medium), Maharashtra Board.
All answers are explained in a simple, step-by-step method to help students understand the concepts easily, complete their homework, and prepare for exams with confidence.
Let's begin with the Let's Recall solutions!

         Chapter 5 : Expansion Formulae

LET'S RECALL

Formulae

1. (a + b)² = a² + 2ab + b²

2. (a - b)² = a² - 2ab + b²

3. (a + b)(a - b) = a² - b²

(i) (x+2y)²

Formula Used: (a+b)²=a²+2ab+b²

Solution:

Take a=x and b=2y.

(x+2y)²=x²+2(x)(2y)+(2y)²

=x²+4xy+4y²

Answer: 4xy

(ii) (2x-5y)²

Formula Used: (a-b)²=a²-2ab+b²

Solution:

Take a=2x and b=5y.

(2x-5y)²=(2x)²-2(2x)(5y)+(5y)²

=4x²-20xy+25y²

Answer: Boxes: 4x², 25y²

(iii) (101)²=(100+1)²=□+□+1²=□

Formula Used: (a+b)²=a²+2ab+b²

Solution:

Here, a=100 and b=1.

(100+1)²=100²+2(100)(1)+1²

=10000+200+1

=10201

Answers:

First Box = 100²

Second Box = 200

Third Box = 10201

(iv) (98)²=(100-2)²=10000-□+□=□

Formula Used: (a-b)²=a²-2ab+b²

Solution:

Here, a=100 and b=2.

(100-2)²=100²-2(100)(2)+2²

=10000-400+4

=9604

Answers:

First Box = 400

Second Box = 4

Third Box = 9604

(v) (5m+3n)(5m-3n)=□-□=□-□

Formula Used: (a+b)(a-b)=a²-b²

Solution:

Here, a=5m and b=3n.

(5m+3n)(5m-3n)=(5m)²-(3n)²

=25m²-9n²

For More Practice Set Solution 

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Practice Set 5.1