MapleInfiniteLimit.mws

>    with(plots):

>    f:=(5*x^4-6*x^2+4*x-9)/(2*x^3-16*x+4);

f := (5*x^4-6*x^2+4*x-9)/(2*x^3-16*x+4)

>    fprime:=diff(f,x);

fprime := (20*x^3-12*x+4)/(2*x^3-16*x+4)-(5*x^4-6*x^2+4*x-9)/(2*x^3-16*x+4)^2*(6*x^2-16)

>    Q:=quo(5*x^4-6*x^2+4*x-9,2*x^3-16*x+4,x);

Q := 5/2*x

>    fGraph:=plot(f,x=-10..10,y=-30..30,thickness=2,discont=true):

>    Qgraph:=plot(5*x/2,x=-10..10,y=-30..30,thickness=2,color=blue):

>    fsolve({2*x^3-16*x+4},{x});

{x = -2.945995202}, {x = .2520003852}, {x = 2.693994817}

>    VertAsym1:=implicitplot(x=-2.945995202,x=-10..10,y=-30..30,thickness=2,color=blue):

>    VertAsym2:=implicitplot(x=0.2520003852,x=-10..10,y=-30..30,thickness=2,color=blue):

>    VertAsym3:=implicitplot(x=2.693994817,x=-10..10,y=-30..30,thickness=2,color=blue):

The function is graphed below in red along with the vertical asymptotes in blue and the slant anymptote in blue.

>    display(fGraph,Qgraph,VertAsym1,VertAsym2,VertAsym3);

[Maple Plot]

>    display(fGraph);

[Maple Plot]

Notice that if we do not set "discont=true" Maple attempts to connect points on each side of a vertical asymptote.  The result is to draw nearly vertical lines that appear to be part

of the graph of the function.

>    fGraph2:=plot(f,x=-10..10,y=-30..30,thickness=2):

>    display(fGraph2);

[Maple Plot]

We can aproximate a relative maximum point and a relative minimum point.

>    fsolve({fprime},{x},-6..-4);

{x = -4.843859207}

>    eval(f,x=-4.843859207);

-17.71869501

>    fsolve({fprime},{x},4..5);

{x = 4.555525404}

>    eval(f,x=4.555525404);

16.95711376

>   

Let's look at a "blow-up" of the graph around the origin.  We can observe two inflection points.

>    plot(f,x=-2.5..2.5,y=-3..3,thickness=2,discont=true);

[Maple Plot]

>    fDoublePrime:=diff(f,x,x);

fDoublePrime := (60*x^2-12)/(2*x^3-16*x+4)-2*(20*x^3-12*x+4)/(2*x^3-16*x+4)^2*(6*x^2-16)+2*(5*x^4-6*x^2+4*x-9)/(2*x^3-16*x+4)^3*(6*x^2-16)^2-12*(5*x^4-6*x^2+4*x-9)/(2*x^3-16*x+4)^2*x

>    fsolve({fDoublePrime},{x},-1..0);

{x = -.7270678089}

>    eval(f,x=-.7270678089);

-.9205088348

>    fsolve({fDoublePrime},{x},0.5..1.5);

{x = .9716981036}

>    eval(f,x=.9716981036);

.6508140006

>