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Ch. 4 - Applications of the Derivative
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243당신이 사용하는 게 아니라요?교과서 변경
4장, 문제 4.3.42

Increasing and decreasing functions. Find the intervals on which f is increasing and the intervals on which it is decreasing.


f(x) = x⁴/4 - 8x³/3 + 15x²/2 + 8

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First, find the derivative of the function f(x) = x⁴/4 - 8x³/3 + 15x²/2 + 8. The derivative, f'(x), will help us determine where the function is increasing or decreasing.
Calculate the derivative: f'(x) = d/dx (x⁴/4 - 8x³/3 + 15x²/2 + 8). Use the power rule for differentiation: d/dx (xⁿ) = n*xⁿ⁻¹.
Simplify the derivative: f'(x) = (4*x³/4) - (8*3*x²/3) + (15*2*x/2). This simplifies to f'(x) = x³ - 8x² + 15x.
Find the critical points by setting the derivative equal to zero: f'(x) = x³ - 8x² + 15x = 0. Factor the equation to find the values of x where the derivative is zero.
Determine the intervals of increase and decrease by testing values from the intervals created by the critical points in the derivative. If f'(x) > 0, the function is increasing; if f'(x) < 0, the function is decreasing.

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Critical Points

Critical points are values of x where the derivative of a function is either zero or undefined. These points are essential for determining where a function changes from increasing to decreasing or vice versa. To find critical points, you first compute the derivative of the function and then solve for x when the derivative equals zero.
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04:50
Critical Points

First Derivative Test

The First Derivative Test is a method used to determine the behavior of a function at its critical points. By analyzing the sign of the derivative before and after each critical point, you can conclude whether the function is increasing or decreasing in the intervals around those points. If the derivative changes from positive to negative, the function is decreasing; if it changes from negative to positive, the function is increasing.
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07:09
The First Derivative Test: Finding Local Extrema

Intervals of Increase and Decrease

Intervals of increase and decrease refer to the ranges of x-values where a function is respectively rising or falling. A function is increasing on an interval if its derivative is positive throughout that interval, while it is decreasing if the derivative is negative. Identifying these intervals helps in understanding the overall behavior of the function and is crucial for graphing and optimization problems.
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07:32
Determining Where a Function is Increasing & Decreasing
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