多项式 满足 的系数为 。方程 的根为 和 。 除以 的余数为 ,除以 的余数为 。
- (a)
求 的表达式。
- (b)
写出清晰的步骤,证明 的实根个数。
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完整解法
6(a)
1. Set up the general form of the polynomial using the given roots and leading coefficient.
Since the roots are and , and are factors of .
Given that the coefficient of is , we can assume is a quartic polynomial of the form:
2. Use the Remainder Theorem to form equations for $p$ and $q$.
By the Remainder Theorem, and .
For :
For :
3. Solve the simultaneous equations to find $p$ and $q$.
Substitute (2) into (1):
Substitute into (2):
4. Write the final expression for $f(x)$.
Substitute and back into the expression for :
6(b)
1. Use the expression for $f(x)$ from part (a) to identify the remaining quadratic factor.
From part (a), we found that .
For , the roots are , , or the roots of .
2. Evaluate the discriminant of the quadratic factor to check for real roots.
For , the discriminant is:
Since the discriminant is less than , has no real roots.
3. State the total number of real roots.
Therefore, the only real roots are and .
There are exactly 2 real roots.
There are exactly 2 real roots.
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