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RS Aggarwal Solutions: Exercise 7C - Factorisation | Mathematics (Maths) Class 8 PDF Download

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Factorise:
x
2
 + 14x + 49
S o l u t i o n :
We have:
      x
2
+14x +49 = x
2
+2 ×x ×7 +(7)
2
                      = (x +7)
2
      ? x
2
+14x +49 = (x +7)
2
                      
Q u e s t i o n : 5 9
Factorise:
1 + 2x + x
2
S o l u t i o n :
We have:
      1 +2x +x
2
= x
2
+2x +1                  = x
2
+2 ×x ×1 +(1)
2
                  = (x +1)
2
     ? 1 +2x +x
2
= (x +1)
2
                  
Q u e s t i o n : 6 0
Factorise:
9 + 6z + z
2
S o l u t i o n :
We have;
      9 +6z +z
2
= z
2
+6z +9                  = z
2
+2 ×x ×3 +(3)
2
                  = (z +3)
2
     ? 9 +6z +z
2
= (z +3)
2
                  
Q u e s t i o n : 6 1
Factorise:
x
2
 + 6ax + 9a
2
S o l u t i o n :
We have:
       x
2
+6ax +9a
2
= x
2
+2 ×x ×3a +(3a)
2
                        = (x +3a)
2
    ? x
2
+6ax +9a
2
= (x +3a)
2
                        
Q u e s t i o n : 6 2
Factorise:
4y
2
 + 20y + 25
S o l u t i o n :
We have:
      4y
2
+20y +25 = (2y)
2
+2 ×2y ×5 +(5)
2
                         = (2y +5)
2
     ? 4y
2
+20y +25 = (2y +5)
2
                         
Q u e s t i o n : 6 3
Factorise:
36a
2
 + 36a + 9
S o l u t i o n :
We have:
      36a
2
+36a +9 = (6a)
2
+2 ×6a ×3 +(3)
2
                      = (6a +3)
2
    ? 36a
2
+36a +9 = (6a +3)
2
                         
Q u e s t i o n : 6 4
Factorise:
9m
2
 + 24m + 16
S o l u t i o n :
We have:
      9m
2
+24m +16 = (3m)
2
+2 ×3m ×4 +(4)
2
                        
                             = (3m +4)
2
     ? 9m
2
+24m +16 = (3m +4)
2
                  
Q u e s t i o n : 6 5
Factorise:
z
2
 + z + 
1
4
S o l u t i o n :
We have:
       z
2
+z +
1
4
= z
2
+2 ×z ×
1
2
×
1
2
2
                       = z +
1
2
2
     ? z
2
+z +
1
4
= z +
1
2
2
Q u e s t i o n : 6 6
Factorise:
49a
2
 + 84ab + 36b
2
S o l u t i o n :
We have:
( )
( )
( )
Page 3


      
  
         
                      
          
      
 
      
                                
       
      
  
       
                                           
      
      
 
      
                             
      
    
 
       
                          
       
   
  
                                                                   
                                     
   
 
                                                              
       
    
 
                         
                          
Factorise:
x
2
 + 14x + 49
S o l u t i o n :
We have:
      x
2
+14x +49 = x
2
+2 ×x ×7 +(7)
2
                      = (x +7)
2
      ? x
2
+14x +49 = (x +7)
2
                      
Q u e s t i o n : 5 9
Factorise:
1 + 2x + x
2
S o l u t i o n :
We have:
      1 +2x +x
2
= x
2
+2x +1                  = x
2
+2 ×x ×1 +(1)
2
                  = (x +1)
2
     ? 1 +2x +x
2
= (x +1)
2
                  
Q u e s t i o n : 6 0
Factorise:
9 + 6z + z
2
S o l u t i o n :
We have;
      9 +6z +z
2
= z
2
+6z +9                  = z
2
+2 ×x ×3 +(3)
2
                  = (z +3)
2
     ? 9 +6z +z
2
= (z +3)
2
                  
Q u e s t i o n : 6 1
Factorise:
x
2
 + 6ax + 9a
2
S o l u t i o n :
We have:
       x
2
+6ax +9a
2
= x
2
+2 ×x ×3a +(3a)
2
                        = (x +3a)
2
    ? x
2
+6ax +9a
2
= (x +3a)
2
                        
Q u e s t i o n : 6 2
Factorise:
4y
2
 + 20y + 25
S o l u t i o n :
We have:
      4y
2
+20y +25 = (2y)
2
+2 ×2y ×5 +(5)
2
                         = (2y +5)
2
     ? 4y
2
+20y +25 = (2y +5)
2
                         
Q u e s t i o n : 6 3
Factorise:
36a
2
 + 36a + 9
S o l u t i o n :
We have:
      36a
2
+36a +9 = (6a)
2
+2 ×6a ×3 +(3)
2
                      = (6a +3)
2
    ? 36a
2
+36a +9 = (6a +3)
2
                         
Q u e s t i o n : 6 4
Factorise:
9m
2
 + 24m + 16
S o l u t i o n :
We have:
      9m
2
+24m +16 = (3m)
2
+2 ×3m ×4 +(4)
2
                        
                             = (3m +4)
2
     ? 9m
2
+24m +16 = (3m +4)
2
                  
Q u e s t i o n : 6 5
Factorise:
z
2
 + z + 
1
4
S o l u t i o n :
We have:
       z
2
+z +
1
4
= z
2
+2 ×z ×
1
2
×
1
2
2
                       = z +
1
2
2
     ? z
2
+z +
1
4
= z +
1
2
2
Q u e s t i o n : 6 6
Factorise:
49a
2
 + 84ab + 36b
2
S o l u t i o n :
We have:
( )
( )
( )
       49a
2
+84ab +36b
2
= (7a)
2
+2 ×7a ×6b +(6b)
2
                                   = (7a +6b)
2
     ? 49a
2
+84ab +36b
2
= (7a +6b)
2
Q u e s t i o n : 6 7
Factorise:
p
2
 - 10p + 25
S o l u t i o n :
We have:
       p
2
-10p +25 = p
2
-2 ×p ×5 +(5)
2
                           = (p -5)
2
      ? p
2
-10p +25 = (p -5)
2
Q u e s t i o n : 6 8
Factorise:
121a
2
 - 88ab + 16b
2
S o l u t i o n :
 We have:
       121a
2
-88ab +16b
2
= (11a)
2
-2 ×11a ×4b +(4b)
2
                                     = (11a -4b)
2
     ? 121a
2
-88ab +16b
2
= (11a -4b)
2
Q u e s t i o n : 6 9
Factorise:
1 - 6x + 9x
2
S o l u t i o n :
 We have:
      1 -6x +9x
2
= 9x
2
-6x +1
                       = (3x)
2
-2 ×3x ×1 +(1)
2
= (3x -1)
2
      ? 1 -6x +9x
2
= (3x -1)
2
Q u e s t i o n : 7 0
Factorise:
9y
2
 - 12y + 4
S o l u t i o n :
 We have:
      9y
2
-12y +4 = (3y)
2
-2 ×3y ×2 +(2)
2
                         = (3y -2)
2
    ? 9y
2
-12y +4 = (3y -2)
2
Q u e s t i o n : 7 1
Factorise:
16x
2
 - 24x + 9
S o l u t i o n :
We have:
       16x
2
-24x +9 = (4x)
2
-2 ×4x ×3 +(3)
2
                           = (4x -3)
2
      ? 16x
2
-24x +9 = (4x -3)
2
Q u e s t i o n : 7 2
Factorise:
m
2
 - 4mn + 4n
2
S o l u t i o n :
We have:
      m
2
-4mn +4n
2
= m
2
-2 ×m ×2n +(2n)
2
                            = (m -2n)
2
     ? m
2
-4mn +4n
2
= (m -2n)
2
Q u e s t i o n : 7 3
Factorise:
a
2
b
2
 - 6abc + 9c
2
S o l u t i o n :
We have:
      a
2
b
2
-6abc +9c
2
= (ab)
2
-2 ×ab ×3c +(3c)
2
                                = (ab -3c)
2
Q u e s t i o n : 7 4
Factorise:
m
4
 + 2m
2
n
2
 + n
4
S o l u t i o n :
We have:
      m
4
+2m
2
n
2
+n
4
= m
2
2
+2 ×m
2
×n
2
+ n
2
2
                              = m
2
+n
2
2
      ? m
4
+2m
2
n
2
+n
4
= m
2
+n
2
2
( ) ( )
( )
( )
Page 4


      
  
         
                      
          
      
 
      
                                
       
      
  
       
                                           
      
      
 
      
                             
      
    
 
       
                          
       
   
  
                                                                   
                                     
   
 
                                                              
       
    
 
                         
                          
Factorise:
x
2
 + 14x + 49
S o l u t i o n :
We have:
      x
2
+14x +49 = x
2
+2 ×x ×7 +(7)
2
                      = (x +7)
2
      ? x
2
+14x +49 = (x +7)
2
                      
Q u e s t i o n : 5 9
Factorise:
1 + 2x + x
2
S o l u t i o n :
We have:
      1 +2x +x
2
= x
2
+2x +1                  = x
2
+2 ×x ×1 +(1)
2
                  = (x +1)
2
     ? 1 +2x +x
2
= (x +1)
2
                  
Q u e s t i o n : 6 0
Factorise:
9 + 6z + z
2
S o l u t i o n :
We have;
      9 +6z +z
2
= z
2
+6z +9                  = z
2
+2 ×x ×3 +(3)
2
                  = (z +3)
2
     ? 9 +6z +z
2
= (z +3)
2
                  
Q u e s t i o n : 6 1
Factorise:
x
2
 + 6ax + 9a
2
S o l u t i o n :
We have:
       x
2
+6ax +9a
2
= x
2
+2 ×x ×3a +(3a)
2
                        = (x +3a)
2
    ? x
2
+6ax +9a
2
= (x +3a)
2
                        
Q u e s t i o n : 6 2
Factorise:
4y
2
 + 20y + 25
S o l u t i o n :
We have:
      4y
2
+20y +25 = (2y)
2
+2 ×2y ×5 +(5)
2
                         = (2y +5)
2
     ? 4y
2
+20y +25 = (2y +5)
2
                         
Q u e s t i o n : 6 3
Factorise:
36a
2
 + 36a + 9
S o l u t i o n :
We have:
      36a
2
+36a +9 = (6a)
2
+2 ×6a ×3 +(3)
2
                      = (6a +3)
2
    ? 36a
2
+36a +9 = (6a +3)
2
                         
Q u e s t i o n : 6 4
Factorise:
9m
2
 + 24m + 16
S o l u t i o n :
We have:
      9m
2
+24m +16 = (3m)
2
+2 ×3m ×4 +(4)
2
                        
                             = (3m +4)
2
     ? 9m
2
+24m +16 = (3m +4)
2
                  
Q u e s t i o n : 6 5
Factorise:
z
2
 + z + 
1
4
S o l u t i o n :
We have:
       z
2
+z +
1
4
= z
2
+2 ×z ×
1
2
×
1
2
2
                       = z +
1
2
2
     ? z
2
+z +
1
4
= z +
1
2
2
Q u e s t i o n : 6 6
Factorise:
49a
2
 + 84ab + 36b
2
S o l u t i o n :
We have:
( )
( )
( )
       49a
2
+84ab +36b
2
= (7a)
2
+2 ×7a ×6b +(6b)
2
                                   = (7a +6b)
2
     ? 49a
2
+84ab +36b
2
= (7a +6b)
2
Q u e s t i o n : 6 7
Factorise:
p
2
 - 10p + 25
S o l u t i o n :
We have:
       p
2
-10p +25 = p
2
-2 ×p ×5 +(5)
2
                           = (p -5)
2
      ? p
2
-10p +25 = (p -5)
2
Q u e s t i o n : 6 8
Factorise:
121a
2
 - 88ab + 16b
2
S o l u t i o n :
 We have:
       121a
2
-88ab +16b
2
= (11a)
2
-2 ×11a ×4b +(4b)
2
                                     = (11a -4b)
2
     ? 121a
2
-88ab +16b
2
= (11a -4b)
2
Q u e s t i o n : 6 9
Factorise:
1 - 6x + 9x
2
S o l u t i o n :
 We have:
      1 -6x +9x
2
= 9x
2
-6x +1
                       = (3x)
2
-2 ×3x ×1 +(1)
2
= (3x -1)
2
      ? 1 -6x +9x
2
= (3x -1)
2
Q u e s t i o n : 7 0
Factorise:
9y
2
 - 12y + 4
S o l u t i o n :
 We have:
      9y
2
-12y +4 = (3y)
2
-2 ×3y ×2 +(2)
2
                         = (3y -2)
2
    ? 9y
2
-12y +4 = (3y -2)
2
Q u e s t i o n : 7 1
Factorise:
16x
2
 - 24x + 9
S o l u t i o n :
We have:
       16x
2
-24x +9 = (4x)
2
-2 ×4x ×3 +(3)
2
                           = (4x -3)
2
      ? 16x
2
-24x +9 = (4x -3)
2
Q u e s t i o n : 7 2
Factorise:
m
2
 - 4mn + 4n
2
S o l u t i o n :
We have:
      m
2
-4mn +4n
2
= m
2
-2 ×m ×2n +(2n)
2
                            = (m -2n)
2
     ? m
2
-4mn +4n
2
= (m -2n)
2
Q u e s t i o n : 7 3
Factorise:
a
2
b
2
 - 6abc + 9c
2
S o l u t i o n :
We have:
      a
2
b
2
-6abc +9c
2
= (ab)
2
-2 ×ab ×3c +(3c)
2
                                = (ab -3c)
2
Q u e s t i o n : 7 4
Factorise:
m
4
 + 2m
2
n
2
 + n
4
S o l u t i o n :
We have:
      m
4
+2m
2
n
2
+n
4
= m
2
2
+2 ×m
2
×n
2
+ n
2
2
                              = m
2
+n
2
2
      ? m
4
+2m
2
n
2
+n
4
= m
2
+n
2
2
( ) ( )
( )
( )
Q u e s t i o n : 7 5
Factorise:
(l + m)
2
 - 4lm
S o l u t i o n :
We have:
    (l +m)
2
-4lm = l
2
+m
2
+2lm -4lm
                         = l
2
+m
2
+2lm -4lm = l
2
+m
2
-2lm = (l)
2
+(m)
2
-2 ×l ×m = (l -m)
2
     ? (l +m)
2
-4lm = (l -m)
2
Q u e s t i o n : 7 6
Factorise:
x
2
 + 5x + 6
S o l u t i o n :
The given expression is x
2
+ 5x + 6. Find two numbers that follow the conditions given below: Sum = 5 Product = 6Clearly, the numbers are 3 and 2. x
2
+ 5x + 6 =  x
2
+ 3x + 2x + 6      
Q u e s t i o n : 7 7
Factorise:
y
2
 + 10y + 24
S o l u t i o n :
The given expression is y
2
+ 10y + 24. Find two numbers that follow the conditions given below: Sum = 10 Product = 24Clearly, the numbers are 6 and 4. y
2
+ 10y + 24 =  y
2
+ 6y + 4y
Q u e s t i o n : 7 8
Factorise:
z
2
 + 12z + 27
S o l u t i o n :
The given expression is z
2
+ 12z + 27. Find two numbers that follow the conditions given below: Sum = 12 Product = 27Clearly, the numbers are 9 and 3. z
2
+ 12z + 27 = z
2
+ 9z + 3z 
Q u e s t i o n : 7 9
Factorise:
p
2
 + 6p + 8
S o l u t i o n :
The given expression is p
2
+ 6p + 8. Find two numbers that follow the conditions given below: Sum = 6 Product = 8Clearly, the numbers are 4 and 2. p
2
+ 6p + 8 =  p
2
+ 4p + 2p +8     
Q u e s t i o n : 8 0
Factorise:
x
2
 + 15x + 56
S o l u t i o n :
The given expression is x
2
+ 15x + 56. Find two numbers that follow the conditions given below: Sum = 15 Product = 56Clearly, the numbers are 8 and 7. x
2
+ 15x + 56 = x
2
+ 8x + 7x 
Q u e s t i o n : 8 1
Factorise:
y
2
 + 19y + 60
S o l u t i o n :
The given expression is y
2
+ 19y + 60. Find two numbers that follow the conditions given below: Sum = 19 Product = 60Clearly, the numbers are 15 and 4. y
2
+ 19y + 60 = y
2
+ 15y + 4
Q u e s t i o n : 8 2
Factorise:
x
2
 + 13x + 40
S o l u t i o n :
The given expression is x
2
+ 13x + 40. Find two numbers that follow the conditions given below: Sum = 13 Product = 40Clearly, the numbers are 8 and 5. x
2
+ 13x + 40 = x
2
+ 8x + 5x 
Q u e s t i o n : 8 3
Factorise:
q
2
 - 10q + 21
S o l u t i o n :
The given expression is q
2
-10q + 21. Find two numbers that follow the conditions given below: Sum = -10 Product = 21Clearly, the numbers are -7 and -3. q
2
-10q + 21 = q
2
-7q -3q + 
Q u e s t i o n : 8 4
Factorise:
p
2
 + 6p - 16
S o l u t i o n :
The given expression is p
2
+ 6p -16. Find two numbers that follow the conditions given below: Sum = 6 Product = -16Clearly, the numbers are 8 and -2. p
2
+ 6p -16 =  p
2
+8p -2p -16   
Q u e s t i o n : 8 5
Factorise:
x
2
 - 10x + 24
S o l u t i o n :
The given expression is x
2
-10x +24. Find two numbers that follow the conditions given below: Sum = -10 Product = 24Clearly, the numbers are -6 and -4. x
2
-10x +24 =  x
2
-6x -4x +24
( )
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