RD Sharma Solutions (Part - 2) - Ex - 7.2, Algebraic Expressions, Class 7, Math Class 7 Notes | EduRev

RD Sharma Solutions for Class 7 Mathematics

Created by: Abhishek Kapoor

Class 7 : RD Sharma Solutions (Part - 2) - Ex - 7.2, Algebraic Expressions, Class 7, Math Class 7 Notes | EduRev

The document RD Sharma Solutions (Part - 2) - Ex - 7.2, Algebraic Expressions, Class 7, Math Class 7 Notes | EduRev is a part of the Class 7 Course RD Sharma Solutions for Class 7 Mathematics.
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QUESTION 9:

Add a3b3 − 3 to the sum of 2a3 − 3b3 − 3ab + 7 and −a3b3 + 3ab −9.

ANSWER 9:

First, we need to find the sum of 2a3 - 3b3 - 3ab + 7 and - a3 + b3 + 3ab - 9.
= (2a3 - 3b3 - 3ab + 7) + (- a3 + b3 + 3ab - 9)
Collecting positive and negative like terms together, we get
= 2a3 - a3- 3b3 + b3 - 3ab + 3ab + 7 - 9
= a3 - 2b3 - 2

Now, the required expression = (a3 + b3 - 3) + (a3 - 2b3 - 2).
                                  = a3 + a3 + b3- 2b3 - 3 - 2
                                  = 2a3 - b3 - 5

QUESTION 10:

Subtract:
 (i) 7a2b from 3a2b
 (ii) 4xy from −3xy

ANSWER 10:

(i) Required expression  =  3a2b - 7a2b
                                        = (3 - 7)a2b
                                        = - 4a2b

(ii) Required expression  = - 3 xy - 4xy
                                         = - 7xy
                                      

QUESTION 11:

Subtract:
 (i) −4x from 3y
 (ii) −2x from −5y

ANSWER 11:

(i) Required expression = (3y) - (-4x)
                                       = 3y + 4x

(ii) Required expression = (-5y) - (-2x)
                                        = -5y + 2x

QUESTION 12:

Subtract:
 (i) 6x3−7x2+5x−3 from 4−5x+6x2−8x36x3-7x2+5x-3 from 4-5x+6x2-8x3
 (ii) −x2−3z from 5x2−y+z+7-x2-3z from 5x2-y+z+7
 (iii) x3+2x2y+6xy2−y3 from y3−3xy2−4x2yx3+2x2y+6xy2-y3 from y3-3xy2-4x2y

ANSWER 12:

(i) Required expression = (4 - 5x + 6x2 - 8x3) - (6x3 - 7x2 + 5x - 3)
                                      = 4 - 5x + 6x2 - 8x3 - 6x3 + 7x2 - 5x + 3
                                      = - 8x3- 6x3 + 7x2 + 6x2- 5x - 5x + 3 + 4
                                      = - 14x3 + 13x2 - 10x +7

(ii) Required expression  = (5x2 - y + z + 7) - (- x2 - 3z)
                                        = 5x2 - y + z + 7 + x2 + 3z
                                        = 5x2+ x2 - y + z + 3z + 7
                                        = 6x2 - y + 4z + 7

(iii) Required expression = (y3 - 3xy2 - 4x2y) - (x3 + 2x2y + 6xy2 - y3)
                                         = y3 - 3xy2 - 4x2y - x3 - 2x2y - 6xy2 + y3
                                         = y3 + y3 - 3xy2- 6xy2 - 4x2y - - x3
                                         = 2y3- 9xy2 - 6x2y - x3

QUESTION 13:

From
 (i) p3 − 4 + 3p2, take away 5p2 − 3p3 + p − 6
 (ii) 7 + xx2, take away 9 + x + 3x2 + 7x3
 (iii) 1 − 5y2, take away y3 + 7y2 + y + 1
 (iv) x3 − 5x2 + 3x + 1, take away 6x2 − 4x3 + 5 + 3x

ANSWER 13:

 (i) Required expression = (p3 - 4 + 3p2) - (5p2 - 3p3 + p - 6)
                                        = p3 - 4 + 3p2 - 5p2 + 3p3 - p + 6
                                        = p3 + 3p3 + 3p2 - 5p2- p - 4+ 6
                                        = 4p3 - 2p2 - p + 2

(ii) Required expression = (7 + x - x2) - (9 + x + 3x2 + 7x3)
                                        = 7 + x - x2 - 9 - x - 3x2 - 7x3
                                        = - 7x3- x2 - 3x2 + 7 - 9
                                        = - 7x3 - 4x2 - 2

(iii) Required expression = (1 - 5y2) - (y3+ 7y2 + y + 1)
                                         = 1 - 5y2 - y3 - 7y2 - y - 1
                                         = - y3- 5y2 - 7y2 - y
                                         = - y3- 12y2 - y

(iv) Required expression = (x3 - 5x2 + 3x + 1) - (6x2 - 4x3 + 5 +3x)
                                         = x3 - 5x2 + 3x + 1 - 6x2 + 4x3 - 5 - 3x
                                         = x3 + 4x3 - 5x2 - 6x2 + 1 - 5
                                         = 5x3 - 11x2 - 4

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