Consider all polynomials with the leading coefficient that give the remainder of when divided by and the remainder when divided by . Among these, find the polynomial of the lowest degree.
Solution
Obviously, the degree of such a polynomial must be at least . If the degree were equal to , this polynomial would have the form of
When dividing by the remainder is , and implies and . But when we divide by the remainder cannot be . We can prove this by calculating , since is precisely the remainder obtained when dividing by .
We conclude that the degree of our polynomial is at least . Let
Again, we have . Hence , . From
we find (we can also deduce this from ). The polynomial is .
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