How do you graph the rational function #f(x)=6/(x^2+x-2)#?

1 Answer
Feb 8, 2015

I would factorize the denominator solving the second degree equation to get:
#f(x)=6/((x+2)(x-1))#
This helps you to "see" the forbidden points, i.e., the points where the denominator becomes zero (you do not want this!!!).
They are:
#x=-2#
#x=1#
Excluding these two values of #x# the other are all allowed.
You can now try to figure out the shape of your graph:
1) for x very big positively or negatively your function gets very small or, better, tends to zero (try to substitute in your function, say, #x=1000# or #x=-1000# you'll find #f(x)~0#);
2) getting near to -2 your function gets very big positively (from the left) and negatively (from the right). You can try it by substituting #-1.999# (on the right of #x=-2#) that gives you #f(x)~-2000# and (on the left of #x=-2#) #x=-2.001# giving #f(x)=2000#. This tendency (for #f(x)# to become very big) is repeated as well when you get near #x=1# (try it!);
3) setting #x=0# gives you #y=-3# which is the y-axis intercept;
At the end your graph looks like:

graph{6/(x^2+x-2) [-10, 10, -5, 5]}

hope it helps