We are given the function $f(x) = \frac{x^3}{(x+1)^2}$. The problem asks us to find the domain, intercepts, first and second derivatives, critical points, intervals of increase and decrease, points of inflection, asymptotes, and then to sketch the curve.

AnalysisCalculusDerivativesDomainInterceptsCritical PointsInflection PointsAsymptotesCurve Sketching
2025/6/21

1. Problem Description

We are given the function f(x)=x3(x+1)2f(x) = \frac{x^3}{(x+1)^2}. The problem asks us to find the domain, intercepts, first and second derivatives, critical points, intervals of increase and decrease, points of inflection, asymptotes, and then to sketch the curve.

2. Solution Steps

(a) Domain:
The function is defined for all xx except where the denominator is zero. The denominator (x+1)2(x+1)^2 is zero when x+1=0x+1=0, so x=1x=-1. Therefore, the domain of ff is all real numbers except x=1x=-1. We can write this as x(,1)(1,)x \in (-\infty, -1) \cup (-1, \infty).
(b) Intercepts:
To find the x-intercepts, we set f(x)=0f(x) = 0. x3(x+1)2=0\frac{x^3}{(x+1)^2} = 0 implies x3=0x^3 = 0, so x=0x=0. Thus, the x-intercept is (0,0)(0,0).
To find the y-intercepts, we set x=0x=0. f(0)=03(0+1)2=01=0f(0) = \frac{0^3}{(0+1)^2} = \frac{0}{1} = 0. Thus, the y-intercept is (0,0)(0,0).
(c) First and second derivatives:
We use the quotient rule to find the first derivative f(x)f'(x). The quotient rule is ddx(uv)=vdudxudvdxv2\frac{d}{dx} \left(\frac{u}{v}\right) = \frac{v\frac{du}{dx} - u\frac{dv}{dx}}{v^2}.
Here, u=x3u = x^3 and v=(x+1)2v = (x+1)^2. So, dudx=3x2\frac{du}{dx} = 3x^2 and dvdx=2(x+1)\frac{dv}{dx} = 2(x+1).
f(x)=(x+1)2(3x2)x3(2(x+1))(x+1)4=(x+1)(3x2(x+1)2x3)(x+1)4=3x3+3x22x3(x+1)3=x3+3x2(x+1)3=x2(x+3)(x+1)3f'(x) = \frac{(x+1)^2(3x^2) - x^3(2(x+1))}{(x+1)^4} = \frac{(x+1)(3x^2(x+1) - 2x^3)}{(x+1)^4} = \frac{3x^3+3x^2-2x^3}{(x+1)^3} = \frac{x^3+3x^2}{(x+1)^3} = \frac{x^2(x+3)}{(x+1)^3}
Now, we find the second derivative f(x)f''(x). Again, we use the quotient rule with u=x3+3x2u = x^3 + 3x^2 and v=(x+1)3v = (x+1)^3.
Then dudx=3x2+6x\frac{du}{dx} = 3x^2 + 6x and dvdx=3(x+1)2\frac{dv}{dx} = 3(x+1)^2.
f(x)=(x+1)3(3x2+6x)(x3+3x2)(3(x+1)2)(x+1)6=(x+1)2[(x+1)(3x2+6x)(x3+3x2)(3)](x+1)6=3x3+6x2+3x2+6x3x39x2(x+1)4=6x(x+1)4f''(x) = \frac{(x+1)^3(3x^2+6x) - (x^3+3x^2)(3(x+1)^2)}{(x+1)^6} = \frac{(x+1)^2[(x+1)(3x^2+6x) - (x^3+3x^2)(3)]}{(x+1)^6} = \frac{3x^3 + 6x^2 + 3x^2 + 6x - 3x^3 - 9x^2}{(x+1)^4} = \frac{6x}{(x+1)^4}
(d) Critical points:
Critical points occur when f(x)=0f'(x) = 0 or f(x)f'(x) is undefined. f(x)=x2(x+3)(x+1)3=0f'(x) = \frac{x^2(x+3)}{(x+1)^3} = 0 when x2(x+3)=0x^2(x+3) = 0, which gives x=0x=0 and x=3x=-3. f(x)f'(x) is undefined when (x+1)3=0(x+1)^3 = 0, which means x=1x=-1. Since x=1x=-1 is not in the domain of ff, we only consider x=0x=0 and x=3x=-3. Thus, the critical points are x=0x=0 and x=3x=-3.
The critical points are (3,f(3))=(3,(3)3(3+1)2)=(3,274)(-3, f(-3)) = (-3, \frac{(-3)^3}{(-3+1)^2}) = (-3, \frac{-27}{4}) and (0,f(0))=(0,0)(0, f(0)) = (0,0).
(e) Intervals of increase and decrease:
We analyze the sign of f(x)=x2(x+3)(x+1)3f'(x) = \frac{x^2(x+3)}{(x+1)^3}.
- For x<3x < -3, x2>0x^2 > 0, x+3<0x+3 < 0, and (x+1)3<0(x+1)^3 < 0, so f(x)=(+)()()=(+)>0f'(x) = \frac{(+)(-)}{(-)} = (+) > 0.
- For 3<x<1-3 < x < -1, x2>0x^2 > 0, x+3>0x+3 > 0, and (x+1)3<0(x+1)^3 < 0, so f(x)=(+)(+)()=()<0f'(x) = \frac{(+)(+)}{(-)} = (-) < 0.
- For 1<x<0-1 < x < 0, x2>0x^2 > 0, x+3>0x+3 > 0, and (x+1)3>0(x+1)^3 > 0, so f(x)=(+)(+)(+)=(+)>0f'(x) = \frac{(+)(+)}{(+)} = (+) > 0.
- For x>0x > 0, x2>0x^2 > 0, x+3>0x+3 > 0, and (x+1)3>0(x+1)^3 > 0, so f(x)=(+)(+)(+)=(+)>0f'(x) = \frac{(+)(+)}{(+)} = (+) > 0.
Thus, ff is increasing on (,3)(-\infty, -3) and (1,)(-1, \infty), and decreasing on (3,1)(-3, -1).
(f) Points of inflection:
Points of inflection occur when f(x)=0f''(x) = 0 or f(x)f''(x) is undefined and the concavity changes sign.
f(x)=6x(x+1)4=0f''(x) = \frac{6x}{(x+1)^4} = 0 when 6x=06x = 0, so x=0x=0. f(x)f''(x) is undefined when (x+1)4=0(x+1)^4=0, or x=1x=-1, which is not in the domain.
We check the sign of f(x)f''(x) around x=0x=0:
- For x<0x < 0 (and x>1x > -1), f(x)<0f''(x) < 0, so the graph is concave down.
- For x>0x > 0, f(x)>0f''(x) > 0, so the graph is concave up.
Since the concavity changes at x=0x=0, (0,0)(0,0) is a point of inflection.
(g) Asymptotes:
Vertical asymptotes occur where the function is undefined. Thus there is a vertical asymptote at x=1x=-1.
To find horizontal asymptotes, we consider the limit as xx approaches infinity.
limxx3(x+1)2=limxx3x2+2x+1=limxx1+2/x+1/x2=\lim_{x \to \infty} \frac{x^3}{(x+1)^2} = \lim_{x \to \infty} \frac{x^3}{x^2+2x+1} = \lim_{x \to \infty} \frac{x}{1+2/x+1/x^2} = \infty.
limxx3(x+1)2=limxx3x2+2x+1=limxx1+2/x+1/x2=\lim_{x \to -\infty} \frac{x^3}{(x+1)^2} = \lim_{x \to -\infty} \frac{x^3}{x^2+2x+1} = \lim_{x \to -\infty} \frac{x}{1+2/x+1/x^2} = -\infty.
Since the limits are infinite, there are no horizontal asymptotes.
To check for slant asymptotes, we perform polynomial division:
x3x2+2x+1=x2+3x+2x2+2x+1\frac{x^3}{x^2+2x+1} = x - 2 + \frac{3x+2}{x^2+2x+1}. As x±x \to \pm \infty, 3x+2x2+2x+10\frac{3x+2}{x^2+2x+1} \to 0. Thus, there is a slant asymptote at y=x2y=x-2.
(h) Plot key points and sketch the curve.
Key points:
Intercept: (0,0)
Critical point: (-3, -27/4) = (-3, -6.75)
Inflection point: (0,0)
Asymptotes: x=-1, y=x-2
Increase: (,3),(1,)(-\infty, -3), (-1, \infty)
Decrease: (3,1)(-3, -1)

3. Final Answer

(a) Domain: x(,1)(1,)x \in (-\infty, -1) \cup (-1, \infty)
(b) Intercepts: (0,0)
(c) f(x)=x2(x+3)(x+1)3f'(x) = \frac{x^2(x+3)}{(x+1)^3}, f(x)=6x(x+1)4f''(x) = \frac{6x}{(x+1)^4}
(d) Critical points: (-3, -27/4) and (0,0)
(e) Increasing: (,3)(1,)(-\infty, -3) \cup (-1, \infty), Decreasing: (3,1)(-3, -1)
(f) Inflection point: (0,0), Concave down for x<0,x1x < 0, x \ne -1, Concave up for x>0x > 0
(g) Asymptotes: Vertical asymptote at x=1x = -1, Slant asymptote at y=x2y = x-2
(h) The sketch is omitted, but should show the points, asymptotes and concavity.

Related problems in "Analysis"

The problem asks for the derivative of the function $f(x) = x^2 \ln x$. We need to find $f'(x)$.

DifferentiationProduct RuleLogarithmic Functions
2025/6/22

We need to find the interval of continuity for the function $f(x) = \frac{1}{\sqrt{x+10}}$.

ContinuityFunctionsIntervalsSquare Roots
2025/6/22

The problem consists of multiple limit calculations. (a) $\lim_{h\to 0} \frac{(2+h)^3 - 8}{h}$ (b) $...

LimitsCalculusLimits at InfinityGreatest Integer FunctionTrigonometric Functions
2025/6/21

We are given a function $f(x) = \frac{x+1}{\lfloor 3x-2 \rfloor}$, where $\lfloor x \rfloor$ represe...

DomainContinuityFloor FunctionLimits
2025/6/21

We are given the function $f(x) = 2x - 1 + \ln(\frac{x}{x+1})$. The problem asks us to find the doma...

Function AnalysisDomainLimitsAsymptotesDerivativesMonotonicityExtreme ValuesTable of VariationsOblique AsymptoteRoot FindingApproximation
2025/6/21

The problem consists of three parts: a) Evaluate the limit $\lim_{x\to 2} \frac{|x-2| + x - 2}{x^2 -...

LimitsHyperbolic FunctionsInverse Hyperbolic Functions
2025/6/19

The problem consists of four independent questions: d) Newton's Law of Cooling: The temperature of a...

Differential EquationsNewton's Law of CoolingFunction AnalysisDefinite IntegralFundamental Theorem of CalculusCalculus
2025/6/19

We are given the function $f(x) = \ln(x^2 + x)$. We need to find the domain of $f$, the x-intercepts...

CalculusLimitsDerivativesDomainAsymptotesConcavityGraphingLogarithmic Differentiation
2025/6/19

The problem consists of defining concepts related to functions, determining the truth of statements ...

LimitsContinuityDifferentiabilityEpsilon-Delta DefinitionPiecewise FunctionsCritical NumbersLocal Minima
2025/6/19

The problem involves analyzing the function $f(x) = 2x - 1 + \ln(\frac{x}{x+1})$. It asks to find th...

Function AnalysisDomainLimitsAsymptotesDerivativesMonotonicityCurve SketchingEquation SolvingNumerical Approximation
2025/6/15