Math Problem Statement

حل السؤال

Find the zeros of the function, the y-intercept, the extrema in the interval [-4, 1], the decreasing intervals, and the positivity conditions for the function f(x) = |(x + 2)^3| - 1.

Solution

To solve the given problem step-by-step, let's analyze the function f(x)=(x+2)31f(x) = |(x + 2)^3| - 1 and answer each of the questions provided.

  1. Finding the zeros of the function f(x)f(x):

    The function f(x)=(x+2)31f(x) = |(x + 2)^3| - 1 will be zero when: (x+2)31=0|(x + 2)^3| - 1 = 0 This simplifies to: (x+2)3=1|(x + 2)^3| = 1 Solving for xx, we consider two cases:

    • Case 1: (x+2)3=1(x + 2)^3 = 1
      • Taking the cube root on both sides, x+2=1x=1x + 2 = 1 \Rightarrow x = -1.
    • Case 2: (x+2)3=1(x + 2)^3 = -1
      • Taking the cube root, x+2=1x=3x + 2 = -1 \Rightarrow x = -3.

    Therefore, the zeros of f(x)f(x) are at x=1x = -1 and x=3x = -3.

  2. Finding the y-intercept of the function:

    The y-intercept occurs when x=0x = 0: f(0)=(0+2)31=81=81=7f(0) = |(0 + 2)^3| - 1 = |8| - 1 = 8 - 1 = 7 So, the y-intercept is at (0,7)(0, 7).

  3. Recording the extrema (maximums) of the function in the interval [4,1][-4, 1]:

    To find the extrema, we should examine the behavior of f(x)f(x) within [4,1][-4, 1] and determine if there are any critical points within this interval.

    • At x=4x = -4: f(4)=(4+2)31=(2)31=81=81=7f(-4) = |(-4 + 2)^3| - 1 = |(-2)^3| - 1 = | -8 | - 1 = 8 - 1 = 7
    • At x=3x = -3 (a zero, so this is a critical point): f(3)=0f(-3) = 0
    • At x=1x = -1 (another zero): f(1)=0f(-1) = 0
    • At x=1x = 1: f(1)=(1+2)31=331=271=26f(1) = |(1 + 2)^3| - 1 = |3^3| - 1 = |27| - 1 = 26

    Therefore, the maximum value in [4,1][-4, 1] occurs at x=1x = 1, where f(1)=26f(1) = 26.

  4. Recording the interval where the function is decreasing and positive in the interval [4,1][-4, 1]:

    To determine where the function is decreasing, we examine the derivative of f(x)f(x) and the behavior of (x+2)3|(x + 2)^3|. The function f(x)f(x) decreases in the interval [4,3][-4, -3], as (x+2)3(x+2)^3 is negative and becomes less negative as xx approaches -3.

  5. Identifying where the function is positive only for x0x \leq 0:

    From the zeros calculated in part 1, the function f(x)f(x) is positive in the interval [4,3)(3,1)(1,1][-4, -3) \cup (-3, -1) \cup (-1, 1] where it is strictly above zero.

  6. Identifying where the function is positive only for x>0x > 0:

    In the interval x>0x > 0, the function is positive for x>0x > 0 as f(x)f(x) \to \infty as xx grows.

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Math Problem Analysis

Mathematical Concepts

Absolute value functions
Polynomial functions
Zeros of a function
Intercepts
Extrema
Intervals of increase and decrease

Formulas

Absolute value function |x|
Cubic function transformation (x + a)^3
Interval analysis for function behavior

Theorems

Absolute value property for determining positivity
Fundamental theorem for finding intercepts and zeros
Derivative test for finding intervals of increase and decrease

Suitable Grade Level

Grade 10