Thursday, 30 April 2015

`y=(x+4)/(x-3)` Graph the function. State the domain and range.

To be able to graph the rational function `y =(x+4)/(x-3)` , we solve for possible asymptotes.

Vertical asymptote exists at `x=a` that will satisfy `D(x)=0 ` on a rational function `f(x)= (N(x))/(D(x))` . To solve for the vertical asymptote, we equate the expression at denominator side to `0` and solve for x.


In `y =(x+4)/(x-3)` , the `D(x) =x-3.`


Then, `D(x) =0 `  will be:


`x-3=0`


`x-3+3=0+3`


`x=3`


The vertical asymptote exists at `x=3` .


To determine the horizontal asymptote for a given function:` f(x) = (ax^n+...)/(bx^m+...),` we follow the conditions:


when `n lt m`     horizontal asymptote: `y=0`


        `n=m `     horizontal asymptote: ` y =a/b `


        `ngtm`       horizontal asymptote: NONE


In `y =(x+4)/(x-3)` , the leading terms are `ax^n=x or 1x^1` and `bx^m=x or 1x^1` . The values `n =1` and `m=1` satisfy the condition: n=m. Then, horizontal asymptote  exists at` y=1/1 ` or `y =1` .


To solve for possible y-intercept, we plug-in `x=0` and solve for `y` .


`y =(0+4)/(0-3)`


`y =4/(-3)`


`y = -4/3 or -1.333`  (approximated value)


Then, y-intercept is located at a point `(0, -1.333)` .


To solve for possible x-intercept, we plug-in `y=0` and solve for `x` .


`0 =(x+4)/(x-3)`


`0*(x-3) =(x+4)/(x-3)*(x-3)`


`0 =x+4`


`0-4=x+4-4`


`-4=x or x=-4`


Then, x-intercept is located at a point `(-4,0)` .


Solve for additional points as needed to sketch the graph.


When `x=2` , the `y = (2+4)/(2-3)=6/(-1)=-6` . point: `(2,-6)`


When `x=4` , the `y =(4+4)/(4-3) =8/1=8` . point:` (4,8)`


When `x=10` , the `y =(10+4)/(10-3)=14/7=2` . point: `(10,2)`


When `x=-16` , the `y =(-16+4)/(-16-3)=-12/(-19)~~0.632` . point: `(-16,0.632)`


Applying the listed properties of the function, we plot the graph as:



You may check the attached file to verify the plot of asymptotes and points.


As shown on the graph, the domain: `(-oo, 3)uu(3,oo)`


and range: `(-oo,1)uu(1,oo).`  


The domain of the function is based on the possible values of `x.` The `x=3` excluded due to the vertical asymptote.


The range of the function is based on the possible values of `y` . The `y=1` is excluded due to the horizontal asymptote. 

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