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f(x)=x^4-x^3-20x^2+50x
We want to write a polynomial function with integral coefficients so that f(x)=0 has the given zeros. 0, -5, 3+i To do so, recall the Complex Conjugates Theorem.
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Complex Conjugates Theorem |
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If f(x) is a polynomial with real coefficients, then the complex roots of f(x)=0 occur in conjugate pairs. |
| Root | Factor |
|---|---|
| 0 | x-0 |
| -5 | x-(-5) |
| 3+i | x-(3+i) |
| 3-i | x-(3-i) |
| Polynomial | f(x)= (x-0) [x-(-5)] [x-(3+i)][x-(3-i)] |
Let's simplify the polynomial by applying the Distributive Property. For simplicity, we will start by multiplying the first two factors and the last two factors separately. (x-0) & * [x-(-5)] [x-(3+i)] & * [x-(3-i)] After we find these products, we will multiply the obtained expressions.
Let's continue by finding the product of the last two factors.
Distribute -1
Add parentheses
(a-b)(a+b)=a^2-b^2
(a-b)^2=a^2-2ab+b^2
i^2=- 1
- (- a)=a
Add terms
Finding the product of these two polynomials will give us the desired polynomial function.
Distribute (x^2+5x)
Distribute x^2
Distribute - 6x
Distribute 10
Add and subtract terms