Follow Magicmen Mens For Mne's Fashion,Style ,Dating,Sex Follow for APTITUDE ,REASONING, DATA INTERPRETATION ,GENERAL KNOWLEDGE google.com, pub-7799856554595592, DIRECT, f08c47fec0942fa0 surds and indices - Mission exam
demo-image

surds and indices

Share This

Surds and Indices

Contents

  1. INTRODUCTION
  2. SURDS
    1. PURE SURDS AND MIXED SURDS
    2. SIMILAR AND DISSIMILAR SURDS
    3. MULTIPLYING SURDS
    4. RATIONALIZATION OF SURDS
    5. COMPARISON OF SURDS
  3. INDICES
    1. RULES OF INDICES
    2. COMPARISON OF INDICES

Surds and Indices


  1. INTRODUCTION

We have come across numbers like , and 54 in the concept of Number Systems. We read there that numbers such as 013_001_1013_073… are irrational numbers. We also learnt about powers and exponents in Number Systems and Number Theory. In this chapter, we will focus on the rules that govern the mathematics of these numbers, and will learn how to manipulate them using the Laws of Indices.

  1. SURDS

A surd is an ‘unresolved’ (meaning it still contains the 013_002 symbol) mathematical expression of an nth root. It can also be defined as an irrational number which is represented as the nth root of a rational number.

For example, an irrational number which represents the nth root of a positive rational number a is a surd and is represented as 013_003 .

An alternate way of representing it is 013_004 (this representation uses indices – we will discuss indices later in this chapter).

The symbol 013_002 is called a radical, the base number a is called the radicand and n is the index of the radical, also known as the order of the surd.

Therefore 013_005 are surds of order 2, 3 and 4 respectively.

013_006 is read as the third root (or the cube root) of 6 and 013_007 is read as the fourth root of 7. If the index of the radical is not given, it is assumed to be 2.

For example, 013_008 is read as the square root (or the second root) of 5.

IMPORTANT:

  • Conditions for a number to be a surd are:

  1. It is a positive irrational number
  1. It is of the type013_003, where a is a positive rational number

    Hence, rational numbers like 013_010 are not surds, because these are not unresolved. 013_011 is equal to +2 and 013_012 is equal to 3.

    Again, 013_013 is equal to 013_014 or +20, hence it is not a surd.

    Also, 013_015 is not a surd, as the radicand itself is not a rational number.

  1. PURE SURDS AND MIXED SURDS

In the surd 013_016, 5 is called the coefficient of the surd. When there is no coefficient in a surd, it is assumed that the coefficient is unity. Surds with unit coefficients are known as pure surds and surds with coefficients other than unity are known as mixed surds.

For example: 013_017 are pure surds whereas 013_018 are mixed surds.

The following rules of radicals are useful to simplify surds:

013_019

013_020

013_021

Example 1:

Convert the following into pure surds:

013_022

013_023

Solution:

We need to convert the given mixed surds into surds where the coefficient is 1. In other words, we have to ‘take the coefficient’ inside the root sign.

013_024

013_025

Example 2:

Convert the following into mixed surds:

013_026

013_027

Solution:

To convert a pure surd into a mixed surd, we have to see if there is any factor of the form an inside the nth root sign.

013_028

013_029

Example 3:

What is the square root of

013_030

Solution:

013_031 013_032

013_033

013_034

013_035

013_036

013_037

013_038

013_039 013_040

013_041

Now,

013_042

013_043

013_044

Also, a + b + c = 3 + 45 + 25 = 73

013_045 013_046013_047

013_048 and vice-versa

Explanation:

013_049

013_050

013_051

013_052

013_053

013_054

013_055

013_056

The same procedure can be followed to prove that

013_057

Example 4:

013_058

Solution:

013_059

013_060

Multiplying the above two equations, we get,

013_061 013_062

013_063

013_064

013_065

By comparing, we get,

100 = a3 + 3ab = a3 + 3a(a2 – 13)

= a3 + 3a3 – 39a = 4a3 – 39a

i.e. a(4a2 – 39) = 100

By trial and error, we get a = 4 and thus b = 42 – 13 = 3

Hence, the cube root of (100 – 51013_066) is (4 –013_066)

  1. SIMILAR AND DISSIMILAR SURDS

Surds which have the same irrational part are known as similar surds (even if their coefficients are different).

Surds with different irrational parts are known as dissimilar surds.

For example, 013_067 and 013_068 are similar surds, whereas 013_069 and 013_070 are dissimilar surds.

We can add or subtract similar surds.

For example,

013_071

013_072

  1. MULTIPLYING SURDS

Surds which have the same index can be multiplied without changing their index. The result of multiplication or division of surds having the same index will also have the same index.

For example, 013_066 and 013_073 can be multiplied, and the result will also have an index of 2. Similarly, 013_074 and 013_075 can be multiplied with the result having index 3. However, 013_076 and 013_075 cannot be multiplied directly as their indices are different; i.e. 2 and 3 respectively.

We multiply or divide such surds without changing the index. For example:

013_077

013_078

We can also multiply similar surds (since similar surds will have the same index). The result of multiplying/dividing two similar surds will always be an integer value.

013_079

Example 5:

Simplify the following:

013_080

013_081

Solution:

013_082

013_083

013_084

013_085

013_086 013_087

  1. RATIONALIZATION OF SURDS

The process of converting a surd to a rational number by multiplying it with a suitable number is called rationalization. To rationalize, we multiply the surd with a rationalizing factor. When the rationalizing factor is multiplied with the surd, we get a rational number.

For example, to rationalize 013_088 we multiply it with 013_088 (the rationalizing factor) to get 013_089 and to rationalize 013_090 we multiply it with 013_066 to get 013_091

It is to be noted that there are always multiple rationalizing factors available. In the above example, we could have also multiplied 013_008 with 013_092 to rationalize it,

since 013_093

  1. RATIONALIZING FACTOR OF A SUM OF SURDS

Consider the term 013_094 which is the sum of two surds. The rationalizing factor for this is 013_095. When we multiply these two terms we get,

013_096

This brings us to the concept of the conjugate. The conjugate of 013_097 is 013_098.

Similarly, the conjugate of 013_099 is 013_097. The conjugate is the rationalizing factor (RF) for a sum of surds of the form image102.

  1. USE OF RATIONALIZATION

Rationalization is mostly used to rationalize the denominator of an expression, if the denominator features a sum of surds.

Example 6:

image103

Solution:

image104

image105

image106

image107

Rationalizing surds can often be simplified by converting the surds to their indices form.

Example 7:

image108

Solution:

image109

image110

image111

image112

image113

To rationalize a fraction such as image114 the following steps are carried out:

  1. Multiply the Numerator & Denominator by image115
  1. Then multiply the Numerator & Denominator by [(x + yz) – 2 image116]

Explanation:

image117

image118

image119

image120

image121

Thus, the expression is rationalized (since the denominator is a rational quantity).

Example 8:

image122

Solution:

image123

image124

image125

image126

Now,

image127

image128

image129

image130

image131

image132

  1. COMPARISON OF SURDS

It is difficult to compare two surds of different indices. The strategy we follow is to change both surds to the same order. We can then compare them by the value of their radicands.

The new index of the two surds is the LCM of the original indices of the surds. The following example should make it clear.

Example 9:

image133

Solution:

The order of the surds is 2 and 3, hence we convert both the surds to surds of order 6 (which is the LCM of 2 and 3).

image134

image135

Now we can say that image136

Hence, image137

REMEMBER:

  • The conversions of 013_076 to image138 and image139 to image140 is done using the rules of indices.

  1. INDICES

Exponential notation is a convenient notation for repeated multiplication. It is generally used when a number is multiplied by itself several times.

Notation: If a is any rational number, then a multiplication a multiplication a multiplication ... n times = an. Here, a is called the base and n is called the exponent or index. The plural of the word index is indices.

For example,

4 multiplication 4 = 42 is read as ‘the square of 4’ or ‘4 to the power 2’, and

5 multiplication 5 multiplication 5 = 53 is read as ‘the cube of 5’ or ‘5 to the power 3’ and

6 multiplication 6 multiplication 6 multiplication 6 = 64 is read as ‘6 raised to the power 4’.

In general, an is read as ‘a raised to the power n’.

  1. RULES OF INDICES

If a and b are non-zero rational numbers and m and n are rational numbers, then

image141

image142

image143

image144

image145

image146

image147

image148

image149

Also, we can observe the following properties of indices.

image150

image151

image152

We would now see a few applications of these rules.

Example 10:

Find the value of or simplify the following using the rules of indices:

image153

image154

image155

image156

image157

image158

image159

image160

image161

Solution:

image162

image163

image164

image165

image166

image167

image168

image169

image170

Example 11:

Solve the following equations:

image171

image172

image173

image174

Solution:

image171

image175

image176

image172

image177

image178

image173

image179

image180

image174

image181

image182

image183

image184

Example 12:

Calculate the values of x in the following equation:

image185

[JMET 2009]

(1) minus4, 9(2) 4, 9

(3) 4, 8(4) 7, 6

Solution:

Since we have,

image185

image186

image187

image188

therefore x2 minus 5x minus 36 = 0

therefore (x minus 9)(x + 4) = 0

therefore x = 9 or x = minus4

Hence, option 1.

Example 13:

Given 2x = 8y + 1 and 9y = 3x – 9; the value of x + y is :

[FMS 2010]

(1) 18(2) 21

(3) 24(4) 27

Solution:

2x = 8y + 1

therefore 2x = (23) y + 1

therefore 2x = 23(y + 1)

therefore x = 3y + 3 …(i)

Consider,

9y = 3x – 9

therefore (32)y = 3 x – 9

therefore 32y = 3 x – 9

therefore 2y = x – 9 …(ii)

Solving (i) and (ii) simultaneously, we get,

x = 21 and y = 6

therefore x + y = 21 + 6 = 27

Hence, option 4.

  1. COMPARISON OF INDICES

To compare, we must try to equate the bases or the indices of the two numbers.

Example 14:

Which is greater?

(i) 3245 or 6310

(ii) (22.5)27 or (7.5)54

Solution:

(i) Now,

3245 = (34 multiplication 22)5 = 320 multiplication 210

Also, 6310 = (32 multiplication 7)10 = 320 multiplication 710

Since 710 > 210, we have 6310 > 3245

(ii) Here, let n = 27; then 2n = 54

image189

image190image191

image192

image193

image194

image195

image196

Pages

undefined