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\( f(x)=3 x^{2}+5 \) a. The minimum value is 5 . The domain is all real numbers and the range is \( y \geq 5 \). The function is decreasing to the left of \( x=0 \) and increasing to the right of \( x=0 \). b. The maximum value is 5 . The domain is all real numbers and the range is \( y \leq 5 \). The function is increasing to the left of \( x=0 \) and decreasing to the right of \( x=0 \). c. The minimum value is -5 . The domain is all real numbers and the range is \( y \geq-5 \). T function is decreasing to the left of \( x=0 \) and increasing to the right of \( x=0 \). d. The maximum value is -5 . The domain is all real numbers and the range is \( y \leq-5 \). function is increasing to the left of \( x=0 \) and decreasing to the right of \( x=0 \).

Ask by Johnson Ruiz. in the United States
Jan 21,2025

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Answer

正确答案是 **a**。 **解释:** 函数 \( f(x) = 3x^2 + 5 \) 是一个开口向上的抛物线,最小值为5,定义域为所有实数,值域为 \( y \geq 5 \)。在 \( x=0 \) 时函数递减,当 \( x > 0 \) 时递增。其他选项的描述有误。

Solution

选项 **a** 是正确的。 **解释:** 对于函数 \( f(x) = 3x^2 + 5 \): 1. **最小值**:由于二次项系数为正(3),抛物线开口向上,因此函数在顶点处取得最小值。顶点的横坐标为 \( x = 0 \),代入函数得最小值 \( f(0) = 5 \)。 2. **定义域**:所有实数,即 \( \mathbb{R} \)。 3. **值域**:因为最小值为5,且抛物线向上延伸,所以 \( y \geq 5 \)。 4. **单调性**: - 当 \( x < 0 \) 时,函数递减。 - 当 \( x > 0 \) 时,函数递增。 其他选项的错误之处: - **选项 b**:错误地将最小值5误认为最大值,且单调性方向相反。 - **选项 c**:错误地将最小值定为-5。 - **选项 d**:错误地将最大值定为-5,且单调性方向相反。 因此,**选项 a** 完全正确。

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The function \( f(x) = 3x^{2} + 5 \) is a classic example of a quadratic function, where the parabola opens upwards since the coefficient of \( x^{2} \) is positive. The vertex, located at \( (0, 5) \), gives the minimum value of 5. This means that the lowest point on the graph is at that vertex, and the function extends infinitely upwards from there, confirming that the range is \( y \geq 5 \). When applying quadratic functions like this in real-world scenarios, they can model various phenomena, such as projectile motion. For instance, if you launch an object upward, the height of the object over time can often be represented by a quadratic equation, which helps predict its maximum height and the time it takes to reach that height. This makes understanding the properties of quadratics essential for fields ranging from physics to engineering!

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