Binomial Theorem
` Factorial Notation :For a natural number n , the factorial
of n is written as n! or ∟n & read as " n factorial " is the
productof n natural numbers from 1 to n .
i.e. n! =n (n-1)(n-2)(n-3)(n-4) ........4 . 3 . 2 . 1
=n (n-1)!
=n.(n-1).(n-2)!
e.g.
0!=1
1!=1
2!=2✕1=2.1=2
3!=3✕2✕1=3.2.1=6
4!=4✕3✕2✕1=4.3.2.1=24
5! =5✕4✕3✕2✕1 =5.4.3.2.1=120
6!=6✕5✕4✕3✕2✕1=6.5.4.3.2.1=720
7! =7✕6✕5✕4✕3✕2✕1=7.6.5.4.3.2.1=5040
......... so on.
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COMBINATION : A Combination of a set of n object taken r
at a time without repetition is known as Combination in Mathematics
i.e. Out of n object if r object is selected at time ,
where order is not important. It is denoted by
nCr or C(n ,r) or nCr .
nCr = n! = n!/r!(n-r)!
r! (n-r)!
e.g. 10C4 =10!/ 4! (10-4)!
= 10.9.8.7.6!
4.3.2.1. 6!
= 10.9.8.7 = 210
4.3.2.1
The Above calculation is according to the defination
of Combination.
The Calculation can also be done like this .
10C4 = 10.9.8.7
4.3.2.1
20C6 = 20.19.18.17.16.15
6.5.4.3.2.1
i.e. If the value of r is 4 then just write
Product of n to (n-3) narural number in the numerator
and Product of 4 natural number from1to 4 in denominator
as in 1st example.
Note : nC0=nCn=1 & nC1=n
Bionomial Theorem :
(a+b)¹ = a + b
(a+b)²= a² +2ab+ b²
(a+b)³= a³ + 3a²b + 3ab² + b³
(a+b)⁴= ?
When the higher powers of (a+b) comes then it
becomes difficult for us to remember. If someone
asks us what is 29th power of (a+b) =?
Then it becomes difficult for us to answer .
At that time we can use Binomial Theorem
to Find Higher Powers of (a+b) or any variable.
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(a+b)ⁿ =nC0aⁿbº +nC1aⁿ⁻¹b¹ +nC2aⁿ⁻²b²+nC3aⁿ⁻³b³ +........+nCnaºbⁿ
For Example :
(a+b)⁴ = 4C0 a⁴ b⁰+4C1a³b¹ +4C2 a²b² +4C3 a¹b³+4C4 a⁰b⁴
= a⁴ b⁰+4C1a³b¹+4C2 a²b² +4C3 a¹b³ +b⁴ (4C0=4C1=1)
(a+b)⁴= a⁴ +4a³b¹ +6a²b² +4a¹b³ +b⁴
Simillarly we can calculate
1) (a+b)⁵
= a⁵+5a⁴b¹ +10 a³b² +10a²b³ +5a¹b⁴+b⁵
2) (a+b)⁶
=a⁶+6a⁵b¹+15a⁴b²+20a³b³+15a²b⁴+6a¹b⁵+b⁶
3) (a+b)⁷
=a⁷+7a⁶b¹+21a⁵b²+35a⁴b³+35a³b⁴+21a²b⁵+7a¹b⁶+b⁷
This way we can calculate any power of (a+b) by using Binomial Expansion.
Note :
1) In the expansion of (a+b)ⁿ contains (n+1) terms .
For Example (a+b)² contain 3 terms , (a+b)³ contains 4 terms & so on .
Expansion contain one more term than the power of expansion.
2) First term is alway aⁿ & last term is bⁿ .
For Example in the expansion of (a+b)² first term is a²
and last term is b².
In Example of (a+b)³ , First term is a³ and last term is b³ so on .
3) In each term , the sum of power of each term
i.e a &b is alway n
For example in the expansion of (a+b)², power of 1st term is 2 ,
in second term sum of power of a & b is 2 and
Power of last term is also 2.
simillarly in (A+b)³& so on
4) In the successive term in the expansion we can
see that power of a decreases by 1 and Power of b increases by one.
Binomial Theorem can used for negative term also .
For example
(a-b)⁴= a⁴-4a³b¹+6 a²b² - 4a¹b³ +b⁴
(a-b)⁵= a⁵-5a⁴b¹+10 a³b²-10a²b³ +5a¹b⁴- b⁵
Here we can note that First term is +ve ,
second term is negative & so on. i.e.
Alternate terms are +ve & -ve .
Binomial can also used for fractional & negative powers also .
1/1+x = (1+x)⁻¹ =1-x+x²-x³+x⁴-x⁵+.......
1/1-x =(1-x)⁻¹ = 1+x+x²+x³+x⁴+x⁵+.......
1/(1+x)² = (1+x)⁻² =1-2x+3x²-4x³+........
1/(1-x)² =(1-x)⁻² =1+2x+3x²+4x³+......
1/√(1+x) =(1+x)⁻¹/² = 1+x/2-x²/8+x³/16+........
1/√(1-x) =(1-x)⁻¹/² = 1-x/2-x²/8-x³/16-.........
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