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If \( f(x)=x^{3}-13 x^{2}+36 x+50 \) and \( x+1 \) is a factor of \( f(x) \), then find all of the zeros of \( f(x) \) algebraically. Answer \( \left.\qquad \begin{array}{l}\oplus \\ \qquad\end{array}\right) \)

Ask by O'Quinn Burgess. in the United States
Mar 13,2025

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Answer

The zeros of \( f(x) \) are \( -1 \), \( 7+i \), and \( 7-i \).

Solution

1. Since \( x+1 \) is a factor of \( f(x)=x^{3}-13x^{2}+36x+50 \), then \( f(-1)=0 \). 2. We perform synthetic division of \( f(x) \) by \( x+1 \) (using \(-1\) as the root): - Coefficients: \( 1 \) (for \( x^3 \)), \( -13 \) (for \( x^2 \)), \( 36 \) (for \( x \)), \( 50 \) (constant). - Write \(-1\) on the left and the coefficients on the top: \[ \begin{array}{c|cccc} -1 & 1 & -13 & 36 & 50 \\ & & -1 & 14 & -50 \\ \hline & 1 & -14 & 50 & 0 \\ \end{array} \] - The bottom row (except the last 0) represents the coefficients of the quotient polynomial: \( x^2-14x+50 \). 3. Factorization of \( f(x) \) is: \[ f(x)=(x+1)(x^{2}-14x+50) \] 4. Next, we solve the quadratic equation \( x^{2}-14x+50=0 \) using the quadratic formula: \[ x=\frac{-b\pm\sqrt{b^{2}-4ac}}{2a}. \] Here, \( a=1 \), \( b=-14 \), and \( c=50 \). 5. Substitute the values: \[ x=\frac{-(-14)\pm\sqrt{(-14)^{2}-4(1)(50)}}{2(1)}=\frac{14\pm\sqrt{196-200}}{2}=\frac{14\pm\sqrt{-4}}{2}. \] 6. Since \(\sqrt{-4}=2i\), the solutions become: \[ x=\frac{14\pm2i}{2}=7\pm i. \] 7. The zeros of \( f(x) \) are: \[ \boxed{-1,\quad 7+i,\quad 7-i.} \]

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To find the zeros of the polynomial \( f(x) = x^3 - 13x^2 + 36x + 50 \) using the fact that \( x + 1 \) is a factor, we can perform polynomial long division or synthetic division of \( f(x) \) by \( x + 1 \). 1. **Synthetic Division**: Set up synthetic division with \( -1 \): - Coefficients: 1 (for \(x^3\)), -13 (for \(x^2\)), 36 (for \(x\)), and 50 (constant). - Division steps: - Bring down the 1. - Multiply -1 by 1, add to -13 to get -14. - Multiply -1 by -14 to get 14, add to 36 to get 50. - Multiply -1 by 50 to get -50, add to 50 to get 0 (remainder). The result of the synthetic division is \( x^2 - 14x + 50 \). 2. **Finding Zeros**: Now we need to factor \( x^2 - 14x + 50 \) and find its zeros. We can use the quadratic formula: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \] where \( a = 1, b = -14, c = 50 \): - Calculate the discriminant: \[ b^2 - 4ac = (-14)^2 - 4(1)(50) = 196 - 200 = -4 \] Since the discriminant is negative, the quadratic has complex roots. 3. **Roots Calculation**: \[ x = \frac{14 \pm \sqrt{-4}}{2} = \frac{14 \pm 2i}{2} = 7 \pm i \] Thus, the zeros of \( f(x) \) are: \[ \boxed{-1, 7+i, 7-i} \]

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