Let n in NN. Suppose polynomials p_0(x), p_1(x),…, p_n(x) in RR_n [x] have degrees 0, 1 , 2 , … , n, respectively. Prove that for alp(x) in RR_n [x] there exist unique a_0, … , a_n in RR such that p(x) = a_0p_0(x)+a_1p_1(x) + ... +a_np_n(x).

Oscar Burton

Oscar Burton

Answered question

2022-10-20

For all n N define
R n [ x ] = { p ( x ) R [ x ] : deg ( p ( x ) ) n } .

Answer & Explanation

Travis Sellers

Travis Sellers

Beginner2022-10-21Added 18 answers

Existence: if deg p n 1 we are done by induction. If deg p = n then there exists a n R such that deg ( p a n p n ) n 1 and apply induction again.
Uniqueness: if
p ( x ) = a 0 p 0 ( x ) + a 1 p 1 ( x ) + + a n p n ( x )
and
p ( x ) = b 0 p 0 ( x ) + b 1 p 1 ( x ) + + b n p n ( x ) ,
then
( a 0 b 0 ) p 0 ( x ) + ( a 1 b 1 ) p 1 ( x ) + + ( a n b n ) p n ( x ) = 0.
In the left hand side X n appears only in p n , so a n b n = 0, and so on.

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