Ncert Solutions For Class 7 Maths Ex 12.2

Ncert Solutions For Class 7 Maths Chapter 12 Ex 12.2

 

Q1: Simplify the terms:

(i) 21a32+7a20a

(ii) x2+13x25x+7x315x

(iii) a(ab)b(ba)

(iv) 3x2yxy(xy+xy)+3xy+yx

(v) 5a2b5a2+3a2b3b2+a2b2+8ab23b2

(vi) (3b2+5b4)(8bb24)

Sol:

(i) 21a32+7a20a=21a+7a20b32

8b32

 

(ii) x2+13x25x+7x315x=7x3+13x2x25x15x

=7x3+12x220x

 

(iii) a(ab)b(ba)=aa+bbb+a

=ab

 

(iv) 3x2yxy(xy+xy)+3xy+yx=3x2yxyx+yxy+3xy+yx

=3xxx+y+y2yxyxy+3xy =x2xy+3xy

 

(v)  5a2b5a2+3a2b3b2+a2b2+8ab23b2

5a2b+3a2b+8ab25a2+a23b2b23b2=8a2b+8ab24a27b2

 

(vi) (3b2+5b4)(8bb24)

3b2+5b48b+b2+4=3b2+b2+5b8b+44 =4b23b

 

Q2: Add:

(i) 3mn,5mn,8mn,4mn

(ii) a8ab,3abb,ba

(iii) 7mn+5,12mn+2,9mn8,2mn3

(iv) a+b3,ba+3,ab+3

(v) 14x+10y12xy13,187x10y+8xy,4xy

(vi) 5m7n,3n4m+2,2m3mn5

(vii) 4x2y,3xy2,5xy2,5x2y

(viii) 3p2q24pq+5,10p2q2,15+9pq+7p2q2

(ix) ab4a,4bab,4a4b

(x) x2y21,y21x2,1x2y2

Sol:

(i) 3mn,5mn,8mn,4mn

3mn+(5mn)+8mn(4mn)=(35+84)mn =(2)mn

 

(ii) a8ab,3abb,ba

a8ab+3abb+ba=aa+bb8ab+3ab =5ab

 

(iii) 7mn+5,12mn+2,9mn8,2mn3

7mn+5+12mn+2+9mn8+2mn3=7mn+12mn+9mn+5+283 =(7+12+9)mn+(5+283)=14mn+2

 

(iv) a+b3,ba+3,ab+3

a+b3+ba+3+ab+3=a+aa+b+bb+3+33 =(1+11)a+(1+11)b+(3+33)=a+b+3

 

(v) 14x+10y12xy13,187x10y+8xy,4xy

=14x7x+10y10y+8xy+4xy12xy+1813=7x+18 =7x+18

 

(vi) 5m7n,3n4m+2,2m3mn5

5m4m+2m7n+3n+253mn=3m4n3mn3

 

(vii) 4x2y,3xy2,5xy2,5x2y

4x2y+(3xy2)+(5xy2)+5x2y=4x2y+5x2y3xy25xy2 =9x2y8xy2

 

(viii) 3p2q24pq+5,10p2q2,15+9pq+7p2q2

3p2q24pq+5+(10p2q2)+15+9pq+7p2q2=3p2q2+7p2q210p2q2+9pq4pq+155 =5pq+10

 

(ix) ab4a,4bab,4a4b

ab4a+4bab+4a4b=4a4a+4b4b+abab =0

 

(x) x2y21,y21x2,1x2y2

x2y21+y21x2+1x2y2=x2x2x2+y2y2y2+111 =x2y21

 

Q3: Subtract:

(i)  5y2 from y2

(ii) 6xy from 12xy

(iii) (ab) from (a+b)

(iv) a(b5) from b(5a)

(v) m2+5mn from 4m23mn+8

(vi) x2+10x5 from 5x10

(vii) 5a27ab+5b2 from 3ab2a22b2

(viii) 4pq5q23p2 from 5p2+3q2pq

 

Sol:

(i) y2(5y2)

    =y2+5y2

=6y2

 

(ii) 12xy6xy

=18xy

 

(iii) (a+b)(ab)

=a+ba+b =2b

 

(iv) b(5a)a(b5)

=5babab+5a =5a+5b2ab

 

(v)  4m23mn+8(m2+5mn)

=4m23mn+8+m25mn =5m28mn+8

 

(vi) 5x10(x2+10x5)

=5x10+x210x+5 =x25x5

 

(vii) 3ab2a22b2(5a27ab+5b2)

=3ab2a22b25a2+7ab5b2 =3ab+7ab2a25a22b25b2 =10ab7a27b2

 

(viii) 5p2+3q2pq(4pq5q23p2)

=5p2+3q2pq4pq+5q2+3p2 =5p2+3p2+3q2+5q2pq4pq =8p2+8q25pq

 

Q4: (a) What should be added to x2+xy+y2 to obtain 2x2+3xy ?

(b) What should be subtracted from 2a+8b+10 to get 3a+7b+16?

 

Sol:

(a) Let a should be added

Then according to the question

x2+xy+y2+a=2x2+3xy

 

a=2x2+3xy(x2+xy+y2)

 

a=2x2+3xyx2xyy2

 

a=2x2x2y2+3xyxy

 

a=x2y2+2xy

Hence the value of a comes out to be x2y2+2xy.

Hence  x2y2+2xy should be added.

 

(b) Let b should be subtracted

Then according to the question,

2a+8b+10q=3a+7b+16

 

2a+8b+10q=3a+7b+16

 

q=2a+8b+10(3a+7b+16)

 

q=2a+8b+10+3a7b16

 

q=2a+3a+8b7b+1016

 

q=5a+b6

 

Q5: What should be taken from 3x2-4y2+5xy+20 to obtain –x2-y2+6xy+20 ?

Sol:

Let a be subtracted

Then according to the question,

3x-4y2+5xy+20 – q= –x2-y2+6xy+20

q=  3x-4y2+5xy+20 -(–x2-y2+6xy+20)

q= 3x2-4y2+5xy+20+x2+y2-6xy-20

q=3x2+x2-4y2+y2+5xy-6xy +20 -20

q=4x2-3y2-xy

Hence, 4x2-3y2-xy should be subtracted in the given equation.

 

Q6:

(a) From the sum of 3x – y + 11 and – y – 11, subtract 3x – y – 11.

(b) From the sum of 4 + 3x and 5 – 4x + 2x, subtract the sum of 3x2 – 5x and –x2 + 2x + 5.

Sol:

(a)According to the question

(3x – y + 11)+( – y – 11)-( 3x – y – 11)= 3x – y + 11 – y – 11- 3x + y + 11

= 3x-3x+y-y+11+11-11

=11

(b) According to question,

(4 + 3x)+( 5 – 4x + 2x2)-( 3x2 – 5x)-( –x2 + 2x + 5)

= 4 + 3x+ 5 – 4x + 2x2– 3x2 + 5x +x2 – 2x – 5

= 3x-4x+5x-2x +2x2– 3x2+x2+4+5-5

= 2x+4

 

Related Links
Ncert Science Book Ncert Maths Book Class 9 Pdf
Class 10 Maths Ncert Book Pdf Ncert Physics Book Of Class 12
Ncert Exemplar Class 10 Solutions class 7 science syllabus ncert
class 8 science syllabus ncert Ncert Exemplar Solutions Class 8 Maths
Ncert Exemplar Class 9 Maths Pdf Download Class 10 Maths Ncert Exemplar Solutions
Ncert Exemplar Class 12 Maths Solutions Pdf Ncert Exemplar Class 8 Science Pdf