Indices & Surds

GETTING STARTED

Key properties of Indices are as follows:

1 .  

eg. 2 -1 = 1/2

 

2. am x an  = am+n

eg. a =3, m=4, n=2.

[For simplicity, we are considering m and n to be integers. They can be any numbers- negative, irrational]

34 x 32 = 81 x 9

= 729

= 36

34 x 32  = 3 (4+2) = 3 6

 

3 .  

eg. a = 6, m = 2, n=3

          

      = 6 -1 = 1/6

4. (am)n  = am.n

 eg. a = 3, m = 2, n=3

       (32)3 = 93 = 729

       = 36

       = 32×3 

Note:  a mn  and  (am)n  are not the same.

   

In  a mn power of a is mn ,

whereas for (am)n  it is m.n

 

Eg.

 

3 23 = 38 whereas

 

(32)3  = 32 x 32 x 32

 

           = 32+2+2

 

           = 36


In the first case, the power is 2 raised to 3, whereas in the second case is 2 times 3.

5. (a.b)n = an. bn

eg.
Let a =13, b = 12, n =2

(13.12)2 = 132 . 122

= 169 x 144

= 24336

6.    ( a⁄ b) n = a n⁄ b n

Eg. a = 6, b =2, n=3

( 6⁄2)3 =     63⁄23

= 216 / 27 

= 8

 

7. a0 = 1

SURDS 

We have seen in numbers that the number of form p/q where p and q are integers and q ≠ 0, then p/q is a rational number.

☛ Surds are irrational numbers that are left in root form (√ ) so as to denote the exact value. They are of the form n √a where a is a rational number and n is a positive number.

Eg. √7 , 3√5

 

☛If bn  = a, then  n√a = b

 n√a denotes nth root of a.

Nth root of a number, a is written as   n√a or a1/n

If n is not mentioned, then it is square root of the given number.

Laws of surds:

1. n√a   =  a1/n

Eg.
√16 = 16 1/2
= 4

 

2. n√ (a.b) = n√ a   x n√ b

eg.   3√ 39 =  3√3  .  3√13

 

 

3 .     

Eg.

 

4.  (n√a)n  =  a

Eg.    4√(81)4  = 81

 

5.  

     =   (a1/n) 1/m

                        =  a1/m.n

eg. 

 

 

6.      (n√a)m       =       (n√am)  

eg. (3√3)4 = (3√81)