Laws of Exponents
The laws of exponents are explained here along with their examples.
1. Multiplying powers with same base
For example: x2 × x3, 23 × 25, (-3)2 × (-3)4
In multiplication of exponents if the bases are same then we need to add the exponents.
Consider the following:
1. 23 × 22= (2 × 2 × 2) × (2 × 2) = 23 + 2 = 25
2. 34 × 32 = (3 × 3 × 3 × 3) × (3 × 3) = 34 + 2 = 36
3. (-3)3 × (-3)4 = [(-3) × (-3) × (-3)] × [(-3) × (-3) × (-3) × (-3)]
= (-3)3 + 4 = (-3)7
4. m5 × m3 = (m × m × m × m × m) × (m × m × m) = m5 + 3 = m8
From the above examples, we can generalize that during multiplication when the bases are same then the exponents are added.
am × an = am+n
In other words, if ‘a’ is a non-zero integer or a non-zero rational number and m and n are positive integers, then
am × an = am + n
Similarly, (a/b)m × (a/b)n = (a/b)m + n
Note:
(i) Exponents can be added only when the bases are same.
(ii) Exponents cannot be added if the bases are not same like
m5 × n7, 23 × 34
For example:
1. 53 ×56
= (5 × 5 × 5) × (5 × 5 × 5 × 5 × 5 × 5)
= 53+6[here the exponents are added]
= 59
2. (-7)10 × (-7)12
= [(-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7)] × [( -7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7) × (-7)].
= (-7)10+12 [exponents are added]
= (-7)22
3. (1/2)4 × ( 1/2)3
=[(1/2) × ( 1/2) × ( 1/2) × ( 1/2)] × [ ( 1/2) × ( 1/2) × ( 1/2)]
=(1/2)4 + 3
=(1/2)7
4. 32 × 35
= 32 + 5
= 37
5. (-2)7 × (-2)3
= (-2)7 + 3
= (-2)10
6. (4/9)3 × (4/9)2
= (4/9)3 + 2
= (4/9)5
We observe that the two numbers with the same base are
multiplied; the product is obtained by adding the exponent.
2. Dividing powers with the same base
For example:
35 ÷ 31, 22 ÷ 21, 5(2) ÷ 53
In division if the bases are same then we need to subtract the exponents.
Consider the following:
27 ÷ 24 = 27/24 = (2 × 2 × 2 × 2 × 2 × 2 × 2)/(2 × 2 × 2 × 2) = 27 - 4
= 23
56 ÷ 52 = 56/52 = (5 × 5 × 5 × 5 × 5 × 5)/(5 × 5) = 56-2 = 54
105 ÷ 103 = 105/103 = (10 × 10 × 10 × 10 × 10)/(10 × 10 × 10) = 105 - 3
= 102
74 ÷ 75 = 74/75 = (7 × 7 × 7 × 7)/(7 × 7 × 7 × 7 × 7) = 74 - 5 = 7-1
Let a be a non zero number, then
a5 ÷ a3 = a5/a3 = (a × a × a × a × a)/(a × a × a) = a5 - 3 = a2
again, a3 ÷ a5 = a3/a5 = (a × a × a)/(a × a × a × a × a) = a-(5 - 3 ) = a-2
Thus, in general, for any non-zero integer a,
am ÷ an = am/an = am - n
Note 1:
Where m and n are whole numbers and m > n;
am ÷ an = am/an = a-(n - m)
Note 2:
Where m and n are whole numbers and m < n;
We can generalize that if ‘a’ is a non-zero integer or a non-zero rational number and m and n are positive integers, such that m > n, then
am ÷ an = am - n if m < n, then am ÷ an = 1/an - m
Similarly, (a/b)m ÷ (a/b)n = (a/b)m -n
For example:
1. 710 ÷ 78 = 710/78
= (7 × 7 × 7 × 7 × 7 × 7 × 7 × 7 × 7 × 7)/(7 × 7 × 7 × 7 × 7 × 7 × 7 × 7)
= 710 - 8 [here exponents are subtracted]
= 72
2. p6 ÷ p1=p6/p1
= (p × p × p × p × p × p)/p
= p6 - 1 [here exponents are subtracted]
= p5
3. 44 ÷ 42 = 44/42
= (4 × 4 × 4 × 4)/(4 × 4)
= 44 - 2 [here exponents are subtracted]
= 42
4. 102 ÷ 104 = 102/104
= (10 × 10)/(10 × 10 × 10 × 10)
= 10-(4 - 2) [See note (2)]
= 10-2
5. 53 ÷ 51
= 53 - 1
= 52
6. 35/32
= 35 - 2
= 33
7. (-5)9/(-5)6
= (-5)9 - 6
= (-5)3
8. (7/2)8 ÷ (7/2)5
= (7/2)8 - 5
= (7/2)3
3. Power of a power
For example: (23)2, (52)6, (32 )-3
In power of a power you need multiply the powers.
Consider the following
(i) (23)4
Now, (23)4 means 23 is multiplied four times
i.e. (23)4 = 23 × 23 × 23 × 23
=23 + 3 + 3 + 3
=212
Note: by law (l), since am × an = am + n.
(ii) (23)2
Similarly, now (23)2 means 23 is multiplied two times
i.e. (23)2 = 23 × 23
= 23 + 3 [since am × an = am + n]
= 26
Note: Here, we see that 6 is the product of 3 and 2 i.e,(23)2 = 23 × 2 = 26
(iii)(4-2)3
Similarly, now (4-2 )3 means 4-2 is multiplied three times
i.e. (4-2)3 =4-2 × 4-2 × 4-2
=4-2 + (-2) + (-2)
=4-2 -2 -2
=4-6
Note: Here, we see that -6 is the product of -2 and 3 i.e, (4-2)3
= 4-2 × 3 =4-6
For example:
1.(32)4 = 32 × 4 = 38
2. (53)6 = 53 × 6 = 518
3. (43)8 = 43 × 8 = 424
4. (am)4 = am × 4 = a4m
5. (23)6 = 23 × 6 = 218
6. (xm)-n = xm × (-n) = x-mn
7. (52)7 = 52 × 7 = 514
8. [(-3)4]2 = (-3)4 × 2 = (-3)8
In general, for any non-integer a, (am)n=am × n =amn.Thus where m and n are whole numbers.
If ‘a’ is a non-zero rational number and m and n are positive integers, then {(a/b)m}n = (a/b) mn
For example:
[(-2/5)3]2
= (-2/5)3 × 2
= (-2/5)6
4. Multiplying powers with the same exponents
For example: 32 × 22, 53 × 73
We consider the product of 42 and 32, which have different bases, but the same exponents.
(i) 42 × 32 [here the powers are same and the bases are different]
= (4 × 4)×(3 × 3)
= (4 × 3)×(4 × 3)
= 12 × 12
= 122
Here, we observe that in 122, the base is the product of bases 4 and 3.
We consider,
(ii) 43 × 23
=(4 × 4 × 4)×(2 × 2 × 2)
=(4 × 2)× ( 4 × 2)× (4 × 2)
=8 × 8 × 8
=83
(iii) We also have, 23 × a3
= (2× 2 × 2)×(a × a × a)
= (2 × a)×(2 × a)×(2 × a)
= (2 × a)3
= (2a)3 [here 2 × a = 2a]
(iv) Similarly, we have, a3 × b3
= (a × a × a)×(b × b × b)
= (a × b)× (a × b)× (a × b)
= (a × b)3
= (ab)3 [here a × b = ab]
Note: In general, for any non-zero integer a, b.
am × bm
= (a × b)m
= (ab)m [here a × b = ab]
Note: Where m is any whole number.
(-a)3 × (-b)3
= [(-a) × (-a) × (-a)]×[(-b) × (-b) × (-b)]
= [(-a) × (-b)]× [(-a) × (-b)]× [(-a) × (-b)]
= [(-a)×(-b)]3
= (ab)3 [here a × b = ab and two negative become positive,
(-) × (-) = +]
5. Negative Exponents
If the exponent is negative we need to change it into positive exponent by writing the same in the denominator and 1 in the numerator.
If ‘a’ is a non-zero integer or a non-zero rational number and m is a positive integers, thena-m is the reciprocal of am, i.e.,
a-m = 1/am, if we take ‘a’ as p/q then (p/q)-m = 1/(p/q)m = (q/p)m
again, 1/a-m = am
Similarly, (a/b)-n = (b/a)n, where n is a positive integer
Consider the following
2-1 = 1/2
2-2 = 1/22 = 1/2 × 1/2 = 1/4
2-3 = 1/23 = 1/2 × 1/2 × 1/2 = 1/8
2-4 = 1/24 = 1/2 × 1/2 × 1/2 × 1/2 = 1/16
2-5 = 1/25 = 1/2 × 1/2 × 1/2 × 1/2 × 1/2 = 1/32
[So in negative exponent we need to write 1 in the numerator and in the denominator 2 multiplied to itself five times as 2-5. In other words negative exponent is the reciprocal of positive exponent]
For example:
1. 10-3
= 1/10-3 [here we can see that 1 is in the numerator and in the denominator 103 as we know that negative exponent is the reciprocal]
= 1/10 × 1/10 × 1/10 [here 10 is multiplied to itself 3 times]
= 1/1000
2. (-2)-4
= 1/(-2)4 [here we can see that 1 is in the numerator and in the denominator (-2)4]
=(- 1/2) × (- 1/2) × (- 1/2) × (- 1/2)
= 1/16
3. 2-5
= 1/25
= 1/2 × 1/2
= 1/4
4. 1/3-4
= 34
= 3 × 3 × 3 × 3
= 81
5. (-7)-3
= 1/(-7)3
6. (3/5-3
= (5/3)3
7. (-7/2)-2
= (-2/7)2
6. Power with exponent zero
If the exponent is 0 then you get the result 1 whatever the base is.
For example: 80, ( a/b)0, m0….
If ‘a’ is a non-zero integer or a non-zero rational number then,
a0 = 1
Similarly, (a/b)0 = 1
Consider the following
a0 = 1[anything to the power 0 is 1]
(a/b)0 = 1
(-2/3)0 = 1
(-3)0 = 1
For example:
1. (2/3)3 × (2/3)-3
= (2/3)3 + (-3) [here we know that am × an = am+ n]
= (2/3)3 - 3
= (2/3)0
= 1
2. 25 ÷ 25
= 25/25
= (2 × 2 × 2 × 2 × 2)/(2 × 2 × 2 × 2 × 2)
= 25 - 5 [here by the law am ÷ an =am - n]
= 20
= 1
3. 40 × 30
= 1 × 1[here as we know anything to the power 0 is 1]
= 1
4. am × a-m
= am - m
= a0
= 1
5. 50 = 1
6. (-4/9)0 = 1
7. (-41)0 = 1
8. (3/7)0 = 1
7. Fractional Exponent
In fractional exponent we observe that the exponent is in fraction form.
Consider the following:
21/1 = 2 (it will remain 2).
21/2 =√2 (square root of 2).
21/3 =∛2 (cube root of 2).
21/4 =∜2 (fourth root of 2).
21/5 =5√2 (fifth root of 2).
For example:
1. a1/n [Here a is called the base and 1/n is called the exponent or power]
= n√a [nth root of a]
2. 31/2= √3 [square root of 3]
3. 51/3 = ∛5 [cube root of 5]
Exponents
Exponents
Laws of Exponents
Rational Exponent
Integral Exponents of a Rational Numbers
Solved Examples on Exponents
Practice Test on Exponents
Exponents - WorksheetsWorksheet on Exponents
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