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• Finally, place the green, blue and red strips to cover the rectangle as shown in Fig. 7.
(4x + 6)
x x x x 1 1 1 1 1 1

x

x

(3x + 4) x

1
1

1

1
Fig. 7

Area of rectangle = (4x + 6) × (3x + 4)
2
Total area of all the strips placed above = 12x + 34x + 24
2
So, ............... × ............... = 12x + 34x + 24
observation:
1. Area of rectangle = (4x + 6) × (........ + ........) 2. Number of green strips = ...............

3. Number of blue strips = ............... 4. Number of red strips = ...............
2
5. (4x + 6) × (3x + 4) = ........ x + ........ x + ........
Repeat this activity to explain the concept of multiplication of two linear algebraic
expressions.

Mental Maths
2
2
2
1. What is the value of x – y + (x + y) at x = 1 and y = –1?
2. What is the constant term of (x – 4)(x + 4)?
1
2 2
3. What is the product of xy and –16x y ?
4
1 1
4. If x + = 2, then what is the value of x + .
2
x x 2
2
5. If area of rectangle is x + 7x + 12 and its breadth is x + 4, then what is its length?
2
2
6. If x + y = 10 and xy = 3, then find the value of x – y?
Mathematics-8 214