try to solve but failed..

Let P(a) be a polynomial in a, such that

7a

^{6}-2a^{5}-3a^{4}+6a^{3}-4a^{2}+6a-P(a)=3a^{5}+6a^{4}-5a^{3}+2a^{2}+3Then

7a

^{6}-2a^{5}-3a^{4}+6a^{3}-4a^{2}+6a - (3a^{5}+6a^{4}-5a^{3}+2a^{2}+3) = P(a)So

P(a)=7a

^{6}-5a^{5}-9a^{4}+11a^{3}-6a^{2}+6a-3