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Find the domain of the function. \[ f(x)=\frac{8}{x^{2}-7 x-98} \] What is the domain of \( f \) ?

Ask by Medina Higgins. in the United States
Feb 25,2025

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Answer

The domain of \( f(x) = \frac{8}{x^{2} - 7x - 98} \) is all real numbers except \( x = -7 \) and \( x = 14 \).

Solution

The domain of a function consists of all the input values (x-values) for which the function is defined. In this function   f(x) = 8/(x² - 7x - 98), the only restriction comes from the denominator. The function is undefined when the denominator is zero. So, we need to find the values of x such that   x² - 7x - 98 = 0. To solve this quadratic equation, we can factor it. We look for two numbers that multiply to -98 and add to -7. The numbers -14 and 7 work because:   (-14) × 7 = -98  and  (-14) + 7 = -7. Thus, the quadratic factors as:   (x - 14)(x + 7) = 0. Setting each factor equal to zero gives:   x - 14 = 0  ⟹ x = 14,   x + 7 = 0  ⟹ x = -7. Since the function is undefined when the denominator is zero, we must exclude x = 14 and x = -7 from the domain. Hence, the domain of f is all real numbers except x = -7 and x = 14. In interval notation, the domain is written as:   (-∞, -7) ∪ (-7, 14) ∪ (14, ∞).

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To find the domain of the function \( f(x) = \frac{8}{x^{2} - 7x - 98} \), we need to determine where the function is defined. This function will be undefined wherever the denominator is zero, so we need to solve: \[ x^{2} - 7x - 98 = 0 \] Using the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), where \( a=1 \), \( b=-7 \), and \( c=-98 \): 1. Calculate the discriminant: \( b^2 - 4ac = (-7)^2 - 4 \cdot 1 \cdot (-98) = 49 + 392 = 441 \) 2. Plug into the quadratic formula: \( x = \frac{7 \pm 21}{2} \) This results in the solutions: \( x = 14 \) and \( x = -7 \). Thus, the function is undefined at \( x = 14 \) and \( x = -7 \). Therefore, the domain of \( f \) is all real numbers except these two points: \[ \text{Domain: } (-\infty, -7) \cup (-7, 14) \cup (14, \infty) \]

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