Powers and Negative Exponents: Rules & Examples

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Exponent is any number raised on a base which can also be seen as a numerical force meaning that the number is multiplied by itself. It is represented by a² where a is base and 2 is its power. This can be read as a raise to power 2. Therefore, the method of writing large numbers in a short form using exponent is known as the exponential form

Keyterms: Power, Exponent, Factor, Base, Number, Exponential form.


Powers and Exponents

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The expression that represents the repetition of the same factor is called power. For example, 5², which means 5 × 5 = 10. The number 5 is called the base, and the number 2 is called the power or exponent. The expectation corresponds to the number of times the base is used as a factor.

Powers and Exponents

Powers and Exponents

Other examples, 42, 58, 77, 103, etc. 

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Negative Exponents

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We know that positive exponents tell us how many times a number is multiplied by itself. Although, a negative exponent tells us how many times we have to multiply the reciprocal of the base number. In other words, a negative element explains how often we have to replicate the base. 

An example of negative exponents is 5-4

Therefore, it can be represented as 1/54.

After solving it we get 1/5 × 1/5 × 1/5 × 1/5 = 1/625.

More examples, 3-4, 2-6, 6-3, 5-7, 8-2, etc. 

Note: If there is no exponent given in a number, its power is the same number which means it is its one time. For example, 2 - In this number, 1 is the power of 2 because 1 cannot be written in the power form.

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Laws of Exponent

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Some of the Laws of Exponents are described below.

Exponents with the same base 

  • When two exponential numbers are multiplied with the same base - N4 × N3= N(4+3)
  • When two exponential numbers are divided with the same base - N4/ N3 = N(4-3)

Power of Powers

When a base has a power of power - (44)2, then the powers will be multiplied with each other. (44)2 = (4)4x2 = 48

Same Exponents but Different Bases

  • When two numbers are multiplied with the same exponents - (44 × 24) = (4×2)4 = 84
  • When two numbers are divided with the same exponents - (44 / 24) = (4/2)4 = 24

Also Read: Multiplication and Division of Integers

Use of Negative Exponents

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  • Exponents are widely used in high-level calculations, which allow you to represent a number or variable that automatically repeats itself a certain number of times. For example, the expression 24 represents a product of 2 × 2 × 2 × 2, which is equal to 16. 
  • Some more applications include understanding the scientific scale as a pH scale or Richter scale, using a scientific note to write very large or very small numbers, and taking measurements.

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Things to Remember

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  • The expression that represents the multiplication of the same number is called power.
  • The negative exponent is defined as the multiplicative inverse of the base, raised to an exponent which is opposite the given exponent.
  • a-2 is also known as the multiplicative inverse of a2.
  • Powers are useful in expressing large expressions.
  • A positive exponent determines how often we should multiply a base number, while a negative exponent determines how many times we should divide a base number.

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Sample Questions

Ques. Find the value of (i) 2-3 (ii) 2/3-4 (2 marks)

Ans. (i) 2-3= ½ × ½ × ½ = ?. 

(ii) 2/3 = 3/2 × 3/2 × 3/2 × 3/2 = 81/ 16.

Ques. Simplify -: (3)6 × (3)-3 (2 marks)

Ans. (3)-6 × (3)3 = (3)-(6-3)

→ 3-3

→ 1/3 × 1/3 × 1/3

→ 1/27.

Ques. Evaluate (i) 3-3 (ii) (½)-4 (NCERT) (2 marks)

Ans. (i) 3-3 = 1/3 × 1/3 = 1/27

(ii) (½)-4 = 2 × 2 × 2 × 2 = 16

Ques. Express the following in exponents and powers - (a). 34500 (b). 1/25 (2 marks)

Ans. (a). 34500 = 345 × 100

→ 345 × 102

→ 3.45 ×102 ×102

(By dividing 345 by 100 and by shifting two decimal places to left and at the same 

time multiplying by 100 or 102)

= 3.45 ×104.

(b). 1/25 = 1/52

 = 5-2 (negative exponent)

Ques. Find the value of (i) 7-3 (ii) 46 (iii) (3/6)-6 (2 marks)

Ans. (i) 7-3 = 1/7 × 1/7× 1/7 = 1/343.

(ii) 46 = 4 × 4 × 4 = 64.

(iii) (3/6)-6 = 6/3 × 6/3 × 6/3 = 216/27. 

Ques. (23 + 32)-3 (2 marks)

Ans. (23 + 32)-3 = (8 + 9)-3

17-3

1/17 × 1/17 × 1/17

→ 1/4913.

Ques. Simplify the following negative exponent - (2/3)-3 + (4)-2 (2 marks)

Ans. (2/3)-3 + (4)-2 = (3/2 × 3/2 × 3/2) + (¼ × ¼) 

= (27/8) + (1/16)

= 54+1/16

= 55/16. 

Simplify the expression - (23 ÷ 22)2 × 2-3 (2 marks)

Ans. (23 ÷ 22)2 × 2-3 = (2(3-2))² × 2-3

= (2)2 × 2-3

= 2(2-3)

= 2-1

= ½. 

Also Read:

CBSE X Related Questions

  • 1.
    In the given figure, $AB \parallel DE$ and $AC \parallel DF$. Show that $\Delta ABC \sim \Delta DEF$. If $BC = 10\text{ cm}$, $EB = CF = 5\text{ cm}$ and $AB = 7\text{ cm}$, then find the length $DE$.


      • 2.
        A bag contains 25 balls. Some of them are yellow and others are green. One ball is drawn at random. If probability of getting a green ball is $3/5$, then find the number of yellow balls.


          • 3.
            A chord of a circle, of radius 14 cm, subtends an angle of $60^\circ$ at the centre. Find the area of the smaller sector and perimeter of the smaller segment.


              • 4.
                Prove that $14 - 2\sqrt{3}$ is an irrational number, given that $\sqrt{3}$ is irrational.


                  • 5.
                    The dimensions of a window are $156\text{ cm} \times 216\text{ cm}$. Arjun wants to put grill on the window creating complete squares of maximum size. Determine the side length of the square and hence find the number of squares formed.


                      • 6.
                        Two water taps together can fill a tank in $8\frac{8}{9}$ hours. The tap of larger diameter takes 4 hours less than the smaller one to fill the tank separately. Find the time in which each tap can separately fill the tank.

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