Is this polynomial familiar?

Algebra Level 3

f ( x ) f(x) is a polynomial with integer coefficients. We have,

f ( 1 ) = 1 f(1)=1

f ( 2 ) = 4 f(2)=4

f ( 3 ) = 9 f(3)=9

f ( 4 ) = 16 f(4)=16

f ( 5 ) = 25 f(5)=25

f ( 6 ) = 36 f(6)=36

f ( 7 ) = 49 f(7)=49

f ( 8 ) = 64 f(8)=64

f ( 9 ) = 81 f(9)=81

f ( 10 ) = 100 f(10)=100

Determine f ( 11 ) f(11) .

100 121 Impossible to Determine 81

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

8 solutions

Michael Mendrin
Aug 17, 2014

This polynomial with integer coefficients

f ( x ) = x 2 + n = 1 10 ( x n ) f(x)={ x }^{ 2 }+\displaystyle\prod _{ n=1 }^{ 10 }{ (x-n) }

yields the same as given, and yet f ( 11 ) = 3628921 f(11)=3628921 . Since more than one such polynomial is possible, the answer is indeterminate.

Awesome problem and solution, solved it in a similar fashion!

Ryan Tamburrino - 6 years, 9 months ago

Sir, isn't your equation valid only if given f ( x ) f(x) has degree 10 10 . ?

Dinesh Chavan - 6 years, 9 months ago

Log in to reply

Samuraiwarm Tsunayoshi gives a more complete answer, but the idea is to show that f ( x ) f(x) isn't unique. It's not limited to degree 10 10 .

Michael Mendrin - 6 years, 9 months ago

Let g ( x ) = f ( x ) x 2 g(x) = f(x) - x^{2}

From the problem, g ( x ) g(x) has the root of 1 , 2 , 3 , . . . , 10 1,2,3,...,10

g ( x ) = ( x 1 ) ( x 2 ) . . . ( x 10 ) h ( x ) g(x) = (x-1)(x-2)...(x-10)h(x) for any polynomial h ( x ) h(x) .

It means that h ( x ) h(x) gives any value for any x x .

Therefore, g ( 11 ) g(11) gives any value, and f ( 11 ) f(11) also gives any value. ~~~

@Samuraiwarm Tsunayoshi I think if I apply Lagrange Interpolation theorem i will get a definite answer,am I right ?

Stephen Thajeb - 4 years, 7 months ago

Log in to reply

Yep, but note that Langrange's Interpolation gives you a polynomial with the least degree. In that case obviously f ( x ) = x 2 f(x) = x^{2} and f ( 11 ) = 121 f(11) = 121 . However, it is not a unique polynomial - more than 1 polynomial is possible. The general form is f ( x ) = x 2 + ( x 1 ) ( x 2 ) . . . ( x 10 ) h ( x ) f(x) = x^{2} + (x-1)(x-2)...(x-10)h(x) , where h ( x ) h(x) is any polynomial, so f ( 11 ) f(11) can be anything dependent on h ( 11 ) h(11) .

Samuraiwarm Tsunayoshi - 4 years, 7 months ago
Noel Lo
May 27, 2015

I feel it is impossible to determine because the question did not specify the degree of f ( x ) f(x) .

Figel Ilham
Feb 20, 2015

The polynomial is not even defined before

how can you say that??

Kislay Raj - 6 years, 3 months ago
Gia Hoàng Phạm
Mar 18, 2019

You haven't give us the degree of the polynomial

Gabriel Chacón
Jan 28, 2019

We know that the polynomial g ( x ) = f ( x ) x 2 g(x)=f(x)-x^2 has at least ten roots ( x n = n x_n=n , where n = 1 , 2 , , 10 n=1,2,\ldots,10 ). This polynomial can yield an indefinite number of values for f ( 11 ) f(11) since we don't know its degree.

Ani B
Jan 9, 2019

Impossible to determine. We have to know the coefficient of the product of factors, and the degree of the function, in order to come to a conclusion about the value of f ( 11 ) f(11) .

Richard Desper
Nov 14, 2016

We have no information about the degree of f f . Thus the system is underdetermined. We are given ten fixed values for f. That would uniquely determine a polynomial of degree 10. But if we allow deg ( f ) 11 \deg(f) \geq 11 , then there are infinitely many solutions in the following sense. For any real number k k , there is a polynomial of degree 11 with the given values for x = 1..10 x=1..10 and f ( 11 ) = k f(11)=k .

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...