How do you find the x intercept of #f(x) = (x^2+9x)/(x^2+3x-4)#?

1 Answer
Feb 3, 2015

The #x#-intercept is when #y=0#

So at first, you only have to look at the top half of the equation -- when this is #0# the whole thing is #0#

Leaves us with #x^2+9x=0#

This can be re-written: #x^2+9x=x(x+9)=0#

So we have two answers:
#x=0 or (x+9)=0->x=-9#

Check the answers against the numerator (it may not be #0#!)
#x=0->x^2+3x-4=-4# which is OK
#x=-9->x^2+3x-4=50# which is also #!=0#