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The standard normal probability function is used to describe many different populations. Its graph is the well-known normal curve. This function is defined below. Give the intervals where the functions is increasing and decreasing. \( f(x)=\frac{1}{\sqrt{5 \pi}} e^{-x^{2} / 4} \)

Ask by Beck Vaughn. in the United States
Feb 27,2025

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Answer

The function \( f(x) = \frac{1}{\sqrt{5\pi}} e^{-x^{2}/4} \) is increasing on the interval \( (-\infty, 0) \) and decreasing on the interval \( (0, \infty) \).

Solution

We start with the function   f(x) = (1/√(5π)) · e^(–x²/4). Since the constant (1/√(5π)) is positive, the behavior of f(x) is determined by the exponential part, e^(–x²/4). Step 1. Differentiate f(x): Let A = 1/√(5π), so   f(x) = A · e^(–x²/4). Using the chain rule, compute the derivative of the exponential function:   d/dx [e^(–x²/4)] = e^(–x²/4) · (d/dx (–x²/4)). Differentiate (–x²/4):   d/dx (–x²/4) = –(1/2)x. Thus, the derivative becomes:   f'(x) = A · e^(–x²/4) · (–(1/2)x) = –(A x)/(2) · e^(–x²/4). Step 2. Analyzing the sign of f'(x): Recall that: • A = 1/√(5π) > 0, • e^(–x²/4) > 0 for all x. Therefore, the sign of f'(x) depends only on –(x/2). • If x < 0, then –(x/2) is positive; hence f'(x) > 0. This implies f is increasing on the interval (–∞, 0). • If x > 0, then –(x/2) is negative; hence f'(x) < 0, which means f is decreasing on the interval (0, ∞). Step 3. Conclusion: The function f(x) is increasing for x in (–∞, 0) and decreasing for x in (0, ∞). The point x = 0 is a local maximum. Thus, the function increases on (–∞, 0) and decreases on (0, ∞).

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The Deep Dive

To determine the intervals where the function \( f(x) = \frac{1}{\sqrt{5 \pi}} e^{-x^{2} / 4} \) is increasing or decreasing, we need to find the derivative \( f'(x) \) and analyze its sign. After computing the derivative, we find \( f'(x) \) which is \( f'(x) = -\frac{x}{2\sqrt{5\pi}} e^{-x^{2}/4} \). The function is decreasing when \( x > 0 \) and increasing when \( x < 0 \). Hence, the intervals are: increasing on \( (-\infty, 0) \) and decreasing on \( (0, \infty) \). Understanding the shape of the normal curve is not only fascinating but essential. This curve is symmetric around the mean (which is zero in a standard normal distribution) and tapers off towards both ends. This characteristic makes it a crucial component in statistics, especially when analyzing data that follow a normal distribution. The standard normal distribution, represented by this function, also has practical applications in various fields, including psychology for scoring IQ tests, finance for assessing risk, and even in quality control in manufacturing. In each case, understanding where the function increases or decreases helps professionals make informed decisions related to probabilities and outcomes based on data distributions!

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