Subham's coefficient sum

Algebra Level 2

What is the sum of the coefficients in the expansion of ( 1 + x ) 5 (1+x)^5 ?

This problem is posed by Subham B .


The answer is 32.

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19 solutions

Mukesh G
Dec 18, 2013

The series forms PASCAL's traingle

                     1

1, 1

1, 2, 1

1, 3, 3, 1

1, 4, 6, 4, 1

1, 5, 10, 10, 5 , 1

Therefore, sum of 1+5+10+10+5+1 = 32

yeh indeed its a pascal 3angle wkwk

Rafi Ramadhana - 7 years, 2 months ago

yup.. it's easier

Abdul Hafizuddin Al-Ghafur - 7 years, 5 months ago

Well, according to the binomial theorem, the sum of the coefficients is

k = 0 5 ( 5 k ) = 32 \sum_{k=0}^{5} \binom{5}{k} = 32

Ewerton Cassiano
Dec 18, 2013

It's a Newton's Binomial, which can be write how: ( 1 + x ) 5 ) (1+x)^5) = k = 1 5 x n k y k ( n k ) \sum_{k=1}^5*x^{n-k}*y^k*(\frac{n}{k}) , where n n = exponent, a a = a, b b = b. So, 1 1 + 5 5 + 10 10 + 10 10 + 5 5 + 1 1 = 32 \boxed{32}

n k \frac{n}{k} need to be the permutation of n n and k k

Ewerton Cassiano - 7 years, 5 months ago

n choose k, instead of n/k and then it makes scene.

Yuliya Skripchenko - 7 years, 5 months ago
Arvind Reddy
Dec 18, 2013

Use Pascal triangle .Since we have 5 in the exponent,we get 6 terms. So we have to use 6th row of Pascal triangle. Since we have 1 and x ,we can directly add the numbers in the 6th row to get the sum of the coefficients. Sixth row of Pascal triangle is 1 5 10 10 5 1 Their sum =1+5+10+10+5+1 = 32

Giuseppe Zecchini
Dec 27, 2013

Let P ( x ) = ( 1 + x ) 5 P(x)=(1+x)^5 , so P ( 1 ) P(1) is the sum of the coefficients of P ( x ) P(x) .

this is simple problem but so hard to find its simple. it use pascal triangle just look at the number of expansion, it's 5. so, 2^5 = 32

Obscure Gilon
Dec 18, 2013

5C1+5C2+5C3+5C4+5C5 =1+5+10+10+5+1 =32 topic: Binomial equation, Combination & permutation.

5C0 missing !!!

Sachin Mourya - 7 years, 4 months ago
Chaitu Sakhare
Feb 3, 2014

just make use of pascal triangle so the coefficients will be 1 5 10 10 5 1 so 1+5+10+10+5+1=32

Raj Gupta
Dec 21, 2013

(1+1)^5=32

why taking 1+1??

Urvashi Joshi - 7 years, 5 months ago
Budi Utomo
Dec 18, 2013

(1+x)^5 = 5C0. X^(5-0) + 5C1. X^(5-1) + 5C2. X^(5-2) + 5C3. X^(5-3) + 5C4. X^(5-4) + 5C5. X^(5-5) = 1x^5 + 5.x^4 + 10x^3 + 10x^2 + 5x + 1. So, sum of all coefficients of (1+x)^5 = 1 + 5 + 10 + 10 + 5 + 1 = 32. Answer : 32

Navneet Mundhra
Apr 14, 2014

for a polynomial, (1+x)^n, the rth co-efficient is rCn........in current case r wil range from 1 to 5 and n = 5....co-efficients are 1, 5, 10, 10, 5, 1 ( 6 terms).........thus sum is 32

Moshiur Mission
Apr 8, 2014

5c0+5c1+5c2+5c3+5c4+5c5 = 32

Rahul Gaur
Mar 7, 2014

(1+x)^5=1+5+10+10+5+1

Prasun Biswas
Feb 22, 2014

We use here the binomial theorem to find the expansion of the expression ( 1 + x ) 5 (1+x)^5 .Also, we must know that the value of the binomial coefficient ( n r ) = n ! r ! × ( n r ) ! \binom{n}{r}=\frac{n!}{r!\times (n-r)!} . From the binomial theorem, we know that ---

( 1 + x ) 5 = ( 5 0 ) + ( 5 1 ) x + ( 5 2 ) x 2 + ( 5 3 ) x 3 + ( 5 4 ) x 4 + ( 5 5 ) x 5 (1+x)^5=\binom{5}{0}+\binom{5}{1}x+\binom{5}{2}x^2+\binom{5}{3}x^3+\binom{5}{4}x^4+\binom{5}{5}x^5

Now, Sum of the coefficients = ( 5 0 ) + ( 5 1 ) + ( 5 2 ) + ( 5 3 ) + ( 5 4 ) + ( 5 5 ) =\binom{5}{0}+\binom{5}{1}+\binom{5}{2}+\binom{5}{3}+\binom{5}{4}+\binom{5}{5}

= 1 + 5 + 10 + 10 + 5 + 1 = 32 =1+5+10+10+5+1 = \boxed{32}

Akshay Mujumdar
Feb 12, 2014

Put x=1 in expansion of (1+x)^n.... You will find that sum of co-efficients is 2^n... Here as n=5, sum of co-efficients is 2^5=32.....

R J
Dec 18, 2013

formula is 2^{n} 2^{5}=32

Israel Smith
Dec 18, 2013

sum C(5,k) , k=0 to 5. Newton Binomial

Vishnudatt Gupta
May 9, 2014

1, 1 (by pascals triangle)

1, 2, 1

1, 3, 3, 1

1, 4, 6, 4, 1

1, 5, 10, 10, 5 , 1

Therefore, sum of 1+5+10+10+5+1 = 32

by binomial expansion as well

1+5+10+10+5+1 = 32

Sagar Singh
Dec 20, 2013

expansion of (1+x)^5=1+ 5x + 10x^2 + 10x^3 + 5x^4 + x^5 now add every coefficients i.e. 1+5+10+10+5+1

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