Chapter 1: Limits
Section 1.6: Continuity
Example 1.6.5
Where is the function Fx=tan(4−x3/4+4⁢x2−2⁢x+3x2+1) continuous?
Solution
Solution Overview
Because of the term x3/4, the interval −∞,0 is excluded from the domain of F.
The graph of F in Figure 1.6.5(a) shows the vertical asymptote whose equation is x=x^≐0.6400732558 and the horizontal asymptote y=tan4≐1.157821282.
Thus, F is continuous on −∞,x^⋃x^,∞.
restart; G := (abs(4-x^(3/4)) + 4*x^2-2*x+3)/(x^2+1): X:=fsolve(G=3*Pi/2,x): F := tan(G): p1:=plot(F,x=0..20,view=[0..20,-4..4],discont=[usefdiscont=true],color=black): p2:=plot([X,t,t=-4..4],color=red,linestyle=dot): p3:=plot(tan(4),x=5..20,color=red,linestyle=dot): p4:=plots:-textplot([12,1.5,typeset(y=tan(4))],font=[Times,12]): plots:-display(p||(1..4),labels=[x,y]);
Figure 1.6.5(a) Graph of Fx for x≥0
Detailed Solution
Recognize Fx as the composition Fx=tangx, where gx=4−x3/4+4⁢x2−2⁢x+3x2+1
Control-drag (or type) gx=… Context Panel: Assign Function
gx=4−x3/4+4⁢x2−2⁢x+3x2+1→assign as functiong
Find the horizontal asymptote: y=limx→∞Fx
Expression palette: Limit operator Context Panel: Evaluate and Display Inline
Context Panel: Approximate≻10
limx→∞tangx = tan⁡4→at 10 digits1.157821282
Find the vertical asymptote
Figure 1.6.5(b) is a graph of gx along with the lines y=k π/2,k=1,3,5. The vertical asymptotes for tanx occur at the odd half-multiples of π, so Figure 1.6.5(b) is drawn to see where gx, the argument of tangx, assumes one of these values. The only one is 3 π/2.
It is also useful to know that g0 = 7, and that the minimum of gx is approximately 3.45, found by applying the Optimization≻Minimize option from the Context Panel:
gx = −4+x3/4+4⁢x2−2⁢x+3x2+1→minimize3.44835673863100434,x=2.36115843528260
G:=(abs(4-x^(3/4)) + 4*x^2-2*x+3)/(x^2+1): p1:=plot([G,Pi/2,3*Pi/2,5*Pi/2],x=0..20,color=[black,red,red,red],view=[0..20,0..8]): p2:=plots:-textplot({[10,2,typeset(y=Pi/2)],[10,5.2,typeset(y=3*Pi/2)],[10,7.3,typeset(y=5*Pi/2)]}): plots:-display(p1,p2);
Figure 1.6.5(b) Graph of gx and y=k π/2,k=1,2,3
Write the equation gx=3 π/2 Context Panel: Solve≻Numerically Solve
gx=3 π/2→solve0.6400732558
The solution of the equation gx=3 π/2 is x^≐0.6400732558, so the location of the vertical asymptote has been determined. The details shown in Figure 1.7.5 have now been confirmed, as has been the conclusion that F is continuous on −∞,x^⋃x^,∞.
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