Tuesday 17 September 2013

`y=(x-1)/(x+5)` Graph the function. State the domain and range.

`y=(x-1)/(x+5)`

First, determine the vertical asymptote of the rational function. Take note that vertical asymptote refers to the values of x that make the function undefined. Since it is undefined when the denominator is zero, to find the VA, set the denominator equal to zero.


`x+5=0`


`x=-5`


Graph this vertical asymptote on the grid. Its graph should be a dashed line. (See attachment.)


Next, determine the horizontal or slant asymptote. To do so, compare the degree of numerator and denominator.


degree of numerator = 1


degree of the denominator = 1


Since they have the same degree, the asymptote is horizontal. To get the equation of HA, divide the leading coefficient of numerator by the leading coefficient of the denominator.


`y=1/1`


`y=1`


Graph this horizontal asymptote on the grid. Its graph should be a dashed line.(See attachment.)


Next, find the intercepts.


y-intercept:


`y=(0-1)/(0+5)`


`y=-1/5`


So the y-intercept is  `(0, -1/5)` .


x-intercept:


`0=(x-1)/(x+5)`


`(x+5)*0=(x-1)/(x+5)*(x+5)`


`0=x-1`


`1=x`


So, the x-intercept is `(1,0)` .


Also, determine the other points of the function. To do so, assign any values to x, except -5. And solve for the y values.


`x=-15, y=(-15-1)/(-15+5) = (-16)/(-10)=8/5`


`x=-11, y=(-11-1)/(-11+5)=(-12)/(-6)=2`


`x=-7, y=(-7-1)/(-7+5)=(-8)/(-2)=4`


`x=-6, y=(-6-1)/(-6+5)=(-7)/(-1)=7`


`x=-3, y=(-3-1)/(-3+5) = (-4)/2=-2`


`x=4, y=(4-1)/(4+5)=3/9`


`x=15, y=(15-1)/(15+5)=14/20=7/10`


Then, plot the points `(-15,8/5)` ,   `(-11,2)` ,   `(-7,4)` ,   `(-6,7)` ,   `(-3,-2)` ,   `(0,-1/5)` ,   `(1,0)` ,   `(4,3/9)` and `(15,7/10)` .


And connect them.


Therefore, the graph of the function is:



Base on the graph, the domain of the function is `(-oo, -5) uu (-5,oo)` . And its range is `(-oo, 1) uu (1,oo)` .

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