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Exponents and Powers




What is exponent and Base?

This can be explained with the below example
Exponents and Base class 8
We know
22 = 2×2
33 = 3×3×3
So it is known how we interact with positive exponent

Negative exponents

Here we will be looking how to interact with these type of expression
2-10
11-1
Here we can see that exponents are negative
Now negative exponents can be converted into positive exponents like this
2-10 = 1/210
11-1= 1/11
So
we can say that for any non-zero integer a,
a-m = 1/am
where m is a positive integer. am    is the multiplicative inverse of a-m
 
Example
a) 2-3
b) 3-2
Solution
As a-m = 1/am
a) 2-3 = ½3 = 1/8
b) 3-2 = 1/32 =1/9
 

How to express the decimal number in exponent form

We already know that any non -decimal number can be expressed in exponent form like below
1215 =1000+ 200 +10 +5 = 1 × 103 + 2 × 102 + 2 × 101 + 5 × 100
So these are all positive exponents
Decimal number can be expressed as exponents also
1215.15 =1000+ 2-00 +10 +5 +.10+.05=  1 × 103 + 2 × 102 + 2 × 101 + 5 × 100 +1/10 + 5/100
=1 × 103 + 2 × 102 + 2 × 101 + 5 × 100 +10-1 + 5 ×10-2
So this has both the negative and positive exponents.

Laws of Exponents

Here are the laws of exponents when a and b are non-zero integers and m, n are any integers.
a-m = 1/am
am / an = am-n
(am )n     = amn
am x bm  = (ab)m
am / bm   = (a/b)m
a0 =1
(a/b)-m =(b/a)m
(1)n = 1 for infinitely many n.
(-1)p =1  for any even integer p
These laws can be used to solve the exponents problems
Example:
(-3)3 × (2/3)3
Solution
(-3)3 × (2/3)3
=(-1)3 × (3)3  × (2)3  × (3)-3   as    am x bm     = (ab)m   and  am / bm       = (a/b)m
= (-1)3 × (2)3
=-8
Important Note
an = 1 only if n = 0. This will work for any a except a = 1 or a = –1. For a = 1, 11 = 12 =13 = 1 or (1)n = 1 for infinitely many n.
For a = –1,(–1)0 = (–1)2 = (–1)4 = (–1)-2 = ... = 1 or (–1)p = 1 for any even integer p.
 
Watch this tutorial for more explanation About exponents and power



Use of Exponents to Express Small Numbers in Standard Form

In previous classes we have learnt how to convert large number into exponents form. We can express small number in the standard exponent form also
Let’s take an example to explain
.00001
Step 1:  Count of Number of places after decimal
Here it is 5
Step 2: On the basis of counting in step 1,the number can be written as
.00001 = 1/100000=1/10 = 1X 10-5
 as am = 1/a-m
Basically the decimal has been moved to the place after digit
Another example would be
.00019
Step 1:  In these cases, we count of Number of places after decimal to the first digit only
Here it is 4
Step 2: On the basis of counting in step 1,the number can be written as
.0001 = 1.9/10000=1.9/10 = 1.9X 10-4
 as am = 1/a-m
Watch this tutorial for more explanation About Use of Exponents to Express Small Numbers in Standard Form

Practice Questions
a) .00156
b) .005402
c) .1234
 

 

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Class 8 Maths Class 8 Science
Reference Books for class 8 Math

Given below are the links of some of the reference books for class 8 Math.

  1. Mathematics Foundation Course for JEE/Olympiad : Class 8 This book can take students maths skills further. Only buy if child is interested in Olympiad/JEE foundation courses.
  2. Mathematics for Class 8 by R S Aggarwal Detailed Mathematics book to clear basics and concepts. I would say it is a must have book for class 8 student.
  3. Pearson Foundation Series (IIT -JEE / NEET) Physics, Chemistry, Maths & Biology for Class 8 (Main Books) | PCMB Combo : These set of books could help your child if he aims to get extra knowledge of science and maths. These would be helpful if child wants to prepare for competitive exams like JEE/NEET. Only buy if you can provide help to the child while studying.
  4. Reasoning Olympiad Workbook - Class 8 :- Reasoning helps sharpen the mind of child. I would recommend students practicing reasoning even though they are not appearing for Olympiad.

You can use above books for extra knowledge and practicing different questions.







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