Real Numbers CBSE Notes, Lectures

CBSE - Real Numbers

  • By: Admin
  • (i) 225 > 135 we always divide greater number with smaller one.

    Divide 225 by 135 we get 1 quotient and 90 as remainder so that
    225= 135 × 1 + 90

    Divide 135 by 90 we get 1 quotient and 45 as remainder so that
    135= 90 × 1 + 45

    Divide 90 by 45 we get 2 quotient and no remainder so we can write it as
    90 = 2 × 45+ 0

    As there are no remainder so divisor 45 is our HCF.


    (ii) 38220 > 196 we always divide greater number with smaller one.


    Divide 38220 by 196 then we get quotient 195 and no remainder so we can write it as
    38220 = 196 × 195 + 0

    As there is no remainder so divisor 196 is our HCF.

    (iii) 867 > 255 we always divide greater number with smaller one.

    Divide 867 by 255 then we get quotient 3 and remainder is 102 so we can write it as
    867 = 255 × 3 + 102

    Divide 255 by 102 then we get quotient 2 and remainder is 51 so we can write it as
    255 = 102 × 2 + 51

    Divide 102 by 51 we get quotient 2 and no remainder so we can write it as
    102 = 51 × 2 + 0

    As there is no remainder so divisor 51 is our HCF.

     

  • By: Admin
  • (i) 225 > 135 we always divide greater number with smaller one.

    Divide 225 by 135 we get 1 quotient and 90 as remainder so that
    225= 135 × 1 + 90

    Divide 135 by 90 we get 1 quotient and 45 as remainder so that
    135= 90 × 1 + 45

    Divide 90 by 45 we get 2 quotient and no remainder so we can write it as
    90 = 2 × 45+ 0

    As there are no remainder so divisor 45 is our HCF.


    (ii) 38220 > 196 we always divide greater number with smaller one.


    Divide 38220 by 196 then we get quotient 195 and no remainder so we can write it as
    38220 = 196 × 195 + 0

    As there is no remainder so divisor 196 is our HCF.

    (iii) 867 > 255 we always divide greater number with smaller one.

    Divide 867 by 255 then we get quotient 3 and remainder is 102 so we can write it as
    867 = 255 × 3 + 102

    Divide 255 by 102 then we get quotient 2 and remainder is 51 so we can write it as
    255 = 102 × 2 + 51

    Divide 102 by 51 we get quotient 2 and no remainder so we can write it as
    102 = 51 × 2 + 0

    As there is no remainder so divisor 51 is our HCF.

     

  • By: Admin
  • Let take a as any positive integer and b = 6.

    Then using Euclid’s algorithm we get a = 6q + r here r is remainder and value of q is more than or equal to 0 and r = 0, 1, 2, 3, 4, 5 because 0 ≤ r < b and the value of b is 6 
    So total possible forms will 6q + 0 , 6q + 1 , 6q + 2,6q + 3, 6q + 4, 6q + 5

    6q + 0
    6 is divisible by 2 so it is a even number 

    6q + 1 
    6 is divisible by 2 but 1 is not divisible by 2 so it is a odd number 

    6q + 2 
    6 is divisible by 2 and 2 is also divisible by 2 so it is a even number 

    6q  +3 
    6 is divisible by 2 but 3 is not divisible by 2 so it is a odd number 

    6q + 4 
    6 is divisible by 2 and 4 is also divisible by 2 it is a even number
     
    6q + 5 
    6 is divisible by 2 but 5 is not divisible by 2 so it is a odd number

    So odd numbers will in form of 6q + 1, or 6q + 3, or 6q + 5

  • By: Admin
  • HCF (616, 32) will give the maximum number of columns in which they can march.
    We can use Euclid's algorithm to find the HCF.
    616 = 32 × 19 + 8
    32 = 8 × 4 + 0
    The HCF (616, 32) is 8.
    Therefore, they can march in 8 columns each.

  • By: Admin
  • HCF (616, 32) will give the maximum number of columns in which they can march.
    We can use Euclid's algorithm to find the HCF.
    616 = 32 × 19 + 8
    32 = 8 × 4 + 0
    The HCF (616, 32) is 8.
    Therefore, they can march in 8 columns each.

  • By: Admin
  • Let a be any positive integer and b = 3.
    Then a = 3q + r for some integer q ≥ 0
    And r = 0, 1, 2 because 0 ≤ r < 3
    Therefore, a = 3q or 3q + 1 or 3q + 2
    Or,
    a2 = (3q)2 or (3q + 1)2 or (3q + 2)2
    a2 = (9q)2 or 9q2 + 6q + 1 or 9q2 + 12q + 4
    = 3 × (3q2) or 3(3q2 + 2q) + 1 or 3(3q2 + 4q + 1) + 1
    = 3k1 or 3k2 + 1 or 3k3 + 1

    Where k1, k2, and k3 are some positive integers
    Hence, it can be said that the square of any positive integer is either of the form 3m or 3m + 1

  • By: Admin
  • Let a be any positive integer and b = 3
    a = 3q + r, where q ≥ 0 and 0 ≤ r < 3
    ∴ a = 3q or 3q + 1 or 3q + 2
    Therefore, every number can be represented as these three forms. There are three cases.
     

    Case 1: When a = 3q,

    a3 = (3q)3 = 27q3 = 9(3q)3 = 9m,
    Where m is an integer such that m = 3q3

    Case 2: When = 3q + 1,
    a3 = (3q +1)3
    a3= 27q3 + 27q2 + 9q + 1
    a3 = 9(3q3 + 3q2 + q) + 1
    a3 = 9m + 1
    Where m is an integer such that m = (3q3 + 3q2 + q)

    Case 3: When a = 3q + 2,
    a3 = (3q +2)3
    a3= 27q3 + 54q2 + 36q + 8
    a3 = 9(3q3 + 6q2 + 4q) + 8
    a3 = 9m + 8
    Where m is an integer such that m = (3q3 + 6q2 + 4q)
     

    Therefore, the cube of any positive integer is of the form 9m, 9m + 1,
    or 9m + 8.

  • By: Admin
  • Let a be any positive integer and b = 3
    a = 3q + r, where q ≥ 0 and 0 ≤ r < 3
    ∴ a = 3q or 3q + 1 or 3q + 2
    Therefore, every number can be represented as these three forms. There are three cases.
     

    Case 1: When a = 3q,

    a3 = (3q)3 = 27q3 = 9(3q)3 = 9m,
    Where m is an integer such that m = 3q3

    Case 2: When = 3q + 1,
    a3 = (3q +1)3
    a3= 27q3 + 27q2 + 9q + 1
    a3 = 9(3q3 + 3q2 + q) + 1
    a3 = 9m + 1
    Where m is an integer such that m = (3q3 + 3q2 + q)

    Case 3: When a = 3q + 2,
    a3 = (3q +2)3
    a3= 27q3 + 54q2 + 36q + 8
    a3 = 9(3q3 + 6q2 + 4q) + 8
    a3 = 9m + 8
    Where m is an integer such that m = (3q3 + 6q2 + 4q)
     

    Therefore, the cube of any positive integer is of the form 9m, 9m + 1,
    or 9m + 8.

  • By: Admin
  • (i) 140 = 2 × 2 × 5 × 7 = 22 × 5 × 7
    (ii) 156 = 2 × 2 × 3 × 13 = 22 × 3 × 13
    (iii) 3825 = 3 × 3 × 5 × 5 × 17 = 32 × 52 × 17
    (iv) 5005 = 5 × 7 × 11 × 13
    (v) 7429 = 17 × 19 × 23

  • By: Admin
  • (i) 26 = 2 × 13
    91 =7 × 13
    HCF = 13
    LCM =2 × 7 × 13 =182
    Product of two numbers 26 × 91 = 2366
    Product of HCF and LCM 13 × 182 = 2366
    Hence, product of two numbers = product of HCF × LCM


    (ii) 510 = 2 × 3 × 5 × 17
    92 =2 × 2 × 23
    HCF = 2
    LCM =2 × 2 × 3 × 5 × 17 × 23 = 23460
    Product of two numbers 510 × 92 = 46920
    Product of HCF and LCM 2 × 23460 = 46920
    Hence, product of two numbers = product of HCF × LCM


    (iii) 336 = 2 × 2 × 2 × 2 × 3 × 7
    54 = 2 × 3 × 3 × 3
    HCF = 2 × 3 = 6
    LCM = 2 × 2 × 2 × 2 × 3 × 3 × 3 × 7 =3024
    Product of two numbers 336 × 54 =18144
    Product of HCF and LCM 6 × 3024 = 18144
    Hence, product of two numbers = product of HCF × LCM

  • By: Admin
  • (i) 12 = 2 × 2 × 3
    15 =3 × 5
    21 =3 × 7
    HCF = 3
    LCM = 2 × 2 × 3 × 5 × 7 = 420

    (ii) 17 = 1 × 17
    23 = 1 × 23
    29 = 1 × 29
    HCF = 1
    LCM = 1 × 17 × 19 × 23 = 11339

    (iii) 8 =1 × 2 × 2 × 2
    9 =1 × 3 × 3
    25 =1 × 5 × 5
    HCF =1
    LCM = 1 × 2 × 2 × 2 × 3 × 3 × 5 × 5 = 1800

  • By: Admin
  • We have the formula that
    Product of LCM and HCF = product of number
    LCM × 9 = 306 × 657
    Divide both side by 9 we get
    LCM = (306 × 657) / 9 = 22338

  • By: Admin
  • If any digit has last digit 10 that means it is divisible by 10 and the factors of 10 = 2 × 5.

    So value 6n should be divisible by 2 and 5 both 6n is divisible by 2 but not divisible by 5 So it can not end with 0.

  • By: Admin
  • 7 × 11 × 13 + 13
    Taking 13 common, we get
    13 (7 x 11 +1 )
    13(77 + 1 )
    13 (78)
    It is product of two numbers and both numbers are more than 1 so it is a composite number.

    7 × 6 × 5 × 4 × 3 × 2 × 1 + 5
    Taking 5 common, we get
    5(7 × 6 × 4 × 3 × 2 × 1 +1)
    5(1008 + 1)
    5(1009)
    It is product of two numbers and both numbers are more than 1 so it is a composite number

  • By: Admin
  • They will be meet again after LCM of both values at the starting point.
    18 = 2 × 3 × 3
    12 = 2 × 2 × 3
    LCM = 2 × 2 × 3 × 3 = 36
    Therefore, they will meet together at the starting point after 36 minutes.

  • By: Admin
  • Let take √5 as rational number
    If a and b are two co prime number and b is not equal to 0.
    We can write √5 = a/b
    Multiply by b both side we get
    b√5 = a
    To remove root, Squaring on both sides, we get
    5b2 = a2 …  (i) 
     

    Therefore, 5 divides a2 and according to theorem of rational number, for any prime number pwhich is divides a2 then it will divide a also.
    That means 5 will divide a. So we can write
    a = 5c
    Putting value of a in equation (i) we get
    5b2 = (5c)2
    5b2 = 25c2
    Divide by 25 we get

    b2/5 = c2

    Similarly, we get that b will divide by 5
    and we have already get that a is divide by 5
    but a and b are co prime number. so it contradicts.
    Hence √5 is not a rational number, it is irrational.

  • By: Admin
  • Let take that 3 + 2√5 is a rational number.
    So we can write this number as
    3 + 2√5 = a/b
    Here a and b are two co prime number and b is not equal to 0
    Subtract 3 both sides we get
    2√5 = a/b – 3
    2√5 = (a-3b)/b
    Now divide by 2, we get
    √5 = (a-3b)/2b
    Here a and b are integer so (a-3b)/2b is a rational number so √5 should be a rational number But √5 is a irrational number so it contradicts.
    Hence, 3 + 2√5 is a irrational number.

  • By: Admin
  • (i) Let take that 1/√2 is a rational number.
    So we can write this number as
    1/√2 = a/b
    Here and b are two co prime number and b is not equal to 0
    Multiply by √2 both sides we get
    1 = (a√2)/b
    Now multiply by b
    b = a√2
    divide by a we get
    b/a = √2
    Here a and b are integer so b/a is a rational number so √2 should be a rational number But √2 is a irrational number so it contradicts.
    Hence, 1/√2 is a irrational number


    (ii) Let take that 7√5 is a rational number.
    So we can write this number as
    7√5 = a/b
    Here a and b are two co prime number and b is not equal to 0
    Divide by 7 we get
    √5 = a/(7b)
    Here a and b are integer so a/7b is a rational number so √5 should be a rational number but √5 is a irrational number so it contradicts.
    Hence, 7√5 is a irrational number.


    (iii) Let take that 6 + √2 is a rational number.
    So we can write this number as
    6 + √2 = a/b
    Here a and b are two co prime number and b is not equal to 0
    Subtract 6 both side we get
    √2 = a/b – 6
    √2 = (a-6b)/b
    Here a and b are integer so (a-6b)/b is a rational number so √2 should be a rational number.

    But √2 is a irrational number so it contradicts.
    Hence, 6 + √2 is a irrational number.

  • By: Admin
  • (i) 13/3125
    Factorize the denominator we get
    3125 =5 × 5 × 5 × 5 × 5 = 55

    So denominator is in form of 5m so it is terminating .


    (ii) 17/8
    Factorize the denominator we get
    8 =2 × 2 × 2 = 23
    So denominator is in form of 2m so it is terminating .


    (iii) 64/455
    Factorize the denominator we get
    455 =5 × 7 × 13
    There are 7 and 13 also in denominator so denominator is not in form of 2m × 5n . so it is not terminating.


    (iv) 15/1600
    Factorize the denominator we get
    1600 =2 × 2 × 2 ×2 × 2 × 2 × 5 × 5 = 26 × 52
    so denominator is in form of 2m × 5n
    Hence it is terminating.


    (v) 29/343
    Factorize the denominator we get
    343 = 7 × 7 × 7 = 73
    There are 7 also in denominator so denominator is not in form of 2m × 5n
    Hence it is non-terminating.


    (vi) 23/(23 × 52)
    Denominator is in form of 2m × 5n
    Hence it is terminating.


    (vii) 129/(22 × 57 × 75 )
    Denominator has 7 in denominator so denominator is not in form of 2m × 5n
    Hence it is none terminating.


    (viii) 6/15
    divide nominator and denominator both by 3 we get 2/5
    Denominator is in form of 5m so it is terminating.

    (ix) 35/50 divide denominator and nominator both by 5 we get 7/10
    Factorize the denominator we get
    10=2 × 5
    So denominator is in form of 2m × 5n so it is terminating.


    (x) 77/210
    simplify it by dividing nominator and denominator both by 7 we get 11/30
    Factorize the denominator we get
    30=2 × 3 × 5
    Denominator has 3 also in denominator so denominator is not in form of 2m × 5n

    Hence it is none terminating

  • By: Admin
  • (i) 13/3125 = 13/55 = 13×25/55×25 = 416/105 = 0.00416 (ii) 17/8 = 17/23 = 17×53/23×53 = 17×53/103 = 2125/103 = 2.125

    (iv) 15/1600 = 15/24×102 = 15×54/24×54×102 = 9375/106 = 0.009375

    (vi) 23/2352 = 23×53×22/23 52×53×22 = 11500/105 = 0.115

    (viii) 6/15 = 2/5 = 2×2/5×2 = 4/10 = 0.4

    (ix) 35/50 = 7/10 = 0.7

  • By: Admin
  • (i) Since this number has a terminating decimal expansion, it is a rational number of the form p/q, and q is of the form 2m × 5n.

    (ii) The decimal expansion is neither terminating nor recurring. Therefore, the given number is an irrational number.
    (iii) Since the decimal expansion is non-terminating recurring, the given number is a rational number of the form p/q, and q is not of the form 2m × 5n.

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