SOLUTION: Please help me solve this equation: Find all asymptotes, intercepts and graph. you must also find all the critical points and inflections points (if any) f(x) = x^3-3x^2-10x/

Algebra.Com
Question 816619: Please help me solve this equation:
Find all asymptotes, intercepts and graph. you must also find all the critical points and inflections points (if any)
f(x) = x^3-3x^2-10x/x^2+5x+6

Answer by Edwin McCravy(20059)   (Show Source): You can put this solution on YOUR website!


f(x) = 

Factor the numerator:     Factor the denominator

    x³-3x²-10x                x²+5x+6                    
    x(x²-3x-10)              (x+3)(x+2)
    x(x+3)(x+2)

f(x) = 

Since (x+3) is a factor of the denominator but not
the numerator, there is an asymptote where x+3=0,
or at x=-3, which is the equation of the vertical
asymptote, where there is a non-removable discontinuite.
 Since (x+2) is a factor of both denominator and numerator,
there is a removable discontinuity where x+2=0, at x=-2.

We may cancel the (x+2)'s as long as we also state that
x≠2

f(x) = , where x≠2

So we graph

y = , leaving a hole at x=2

There is a vertical asymptote at x=-3
Since the degree of the numberator is 1 more than the degree
of the denominator, there is no horizontal asymptote, but there
is an oblique (or slant) asymptote, which we find by long
division:

We have to multiply the numerator out and add +0 to divide:

y = ,

        x- 8+
x+3)x²-5x+ 0
    x²+3x
      -8x+ 0
      -8x-24
          34

Since the fraction  approaches 0 as x gets large,
the graph of f(x) must approach the line y=x-8, which is the
equation of the oblique (slant) asymptote.

We get the y-intercept by setting x = 0

y =  = 0

So the y-intercept is (0,0)

We get the x-intercepts by setting y = 0 

0 = 

0 = x(x-5)
    x=0;  x-5=0
            x=5

So the x-intercepts are (0,0) and (5,0)

We plot the asymptotes and the intercepts:


 

Now we find any relative extrema points by
finding the derivative and setting it = 0

y = 
Multiply the top out:
y = 
Use the quoptient formula for the derivative:
y' = 
y' = 
y' = 
Setting that = 0 to find relative extrema:
 = 0
x²+6x-15 = 0
Unfortunately that doesn't factor, so we must
use the quadratic formula:







x = -3 ± 2V6
Approximating:  x=-7.90 and x=1.90
Substuting those in y, we get approximately
                y=-20.8 and y=-1.20

Relative extrema candidates are approximately (-7.90,-20.8)
and (1.90,-1.20)

To find out whether they are relative maximums or minimums,
or any inflection points, we must find the second derivative:

y' = 
Use the quotient formula:
y" = 
y" = 
y" =   
y" = 
y" = 
y" = 
y" = 

Substituting x=-7.90, y" comes out negative,
therefore the point (-7.90,-20.8) is a relative
maximum, since the curvature is downward

Substituting x=1.90, y" comes out positive,
therefore the point (1.90,-1.20) is a relative
minimum, since the curvature is upward
 
To find any inflection points we set y"=0

 = 0
48 = 0
A contradiction so there are no inflection points.

So we draw the graph:

 

What a terribly long and messy problem!

Edwin

RELATED QUESTIONS

Could someone please help me with this problem? Graph y=2^x-3. Label all x-intercepts, (answered by funmath)
I am working on a packet where we have to graph rational functions given only a formula.... (answered by solver91311)
Can you help me? I need to find all intercepts, and all asymptotes. Show work. For this... (answered by CubeyThePenguin)
Find the x- and y- intercepts and graph the equation plotting the intercepts. Please show (answered by oscargut)
Find all the asymptotes, x-intercepts, and y-intercepts for the graph of the given... (answered by CubeyThePenguin,ikleyn)
Please find all appropriate critical points and graph (conic) f(x)= x^2+x-2 Please... (answered by checkley77)
Given the rational function f(x)=2x/x+4 I need to find the domain,find the equation of... (answered by edjones)
Please help with this problem: Find the x- and y- intercepts and graph the equation... (answered by ewatrrr)
Please help!!! Find the critical values,points of inflection and discuss the concavity (answered by Boreal)