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f(x)=x^3-4x^2-15x+68
We want to write a polynomial function with integral coefficients so that f(x)=0 has the given zeros.
-4, 4+i
To do so, recall the Complex Conjugates Theorem for complex zeros.
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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. |
This theorem states that if a + bi is a complex root, then a- bi is also a zero. Additionally, recall that if a is a zero of f(x)=0, then (x-a) is a factor of f(x).
| Root | Factor |
|---|---|
| -4 | x-(-4) |
| 4+i | x-(4+i) |
| 4-i | x-(4-i) |
| Polynomial | f(x)= [x-(-4)] [x-(4+i)] [x-(4-i)] |
Let's simplify the polynomial by applying the Distributive Property. For simplicity, we will start by multiplying the first two factors and then we will multiply the result by the last factor.
- (- a)=a
Distribute -1
Distribute (x-4-i)
Distribute (x-4+i)
i^2=- 1
- (- a)=a
- a(- b)=a* b
Add and subtract terms