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Mathematics 19 Online
OpenStudy (dobby1):

@phi

OpenStudy (phi):

can you factor the top and the bottom (and please repost the fraction)

OpenStudy (dobby1):

|dw:1391638819424:dw|

OpenStudy (dobby1):

if you factor it you get -5x+6/-1

OpenStudy (phi):

the bottom is a "difference of squares" a^2 - b^2 it factors into (a+b)(a-b)

OpenStudy (dobby1):

of yeah ok I will do that

OpenStudy (dobby1):

?/(x+1)(x-1) I have no Idea how to factor the top I tried it another question with that same equation either on the top or bottom

OpenStudy (phi):

to factor a quadratic, look at the last number +6 the + means the factors will have the *same sign* (- means different signs) now list all pairs of numbers that when you multiply them give you 6: 1,6 2,3 (nice short list) next, look at the number in front of the x: -5 the - means the largest factor is - (+ would mean the largest factor is +) from the first step, we know both factors have the same sign... both will be - look at our list with both numbers assigned - and add them. Do any add up to -5 ? -1-6= -7 no -2 - 3= -5 yes. -2 and -3 are our guys. we write (x -2)(x-3)

OpenStudy (dobby1):

ok so how would we graph this

OpenStudy (phi):

You probably skipped that lesson... but math builds on the earlier stuff... if you don't learn each step you will get stuck

OpenStudy (phi):

ok you now have \[ y = \frac{(x-2)(x-3)}{(x+1)(x-1)} \] the zeros (where y=0 and the curve crosses the x-axis) happens when either of the top terms is zero. what x values cause y to be 0?

OpenStudy (dobby1):

uhm -1, 1, 2, and 3 right?

OpenStudy (phi):

only when the top is 0

OpenStudy (dobby1):

ok so then it is 2 and 3

OpenStudy (phi):

ok, make a note: zeros at x=2 and x=3 can you find the horizontal asymptote ?

OpenStudy (dobby1):

uhm idk what to do how would I reduce that fraction

OpenStudy (phi):

you do the same thing we did on the other problem...or was that your twin working that problem ?

OpenStudy (dobby1):

hahaha yeah I know but when I do that the x's should disapear right?

OpenStudy (phi):

yes, we just get y = # (ratio of the coefficients of the highest order term)

OpenStudy (dobby1):

ok but when we get rid of the x's the denominator becomes 0 because of 1-1

OpenStudy (phi):

using only the high order terms you get \[ y = \frac{x^2}{x^2} = 1\\ y=1\]

OpenStudy (dobby1):

oh yeah ok so the horizontal is 1?

OpenStudy (phi):

yes y=1 next, what are the vertical asymptotes ? (where you divide by 0)

OpenStudy (dobby1):

-5/0 right?

OpenStudy (phi):

you have \[ y = \frac{(x-2)(x-3)}{(x-1)(x+1)} \] what x's cause a divide by 0 ?

OpenStudy (dobby1):

bottom

OpenStudy (phi):

yes, but specifically what x values ?

OpenStudy (dobby1):

1 and -1

OpenStudy (phi):

ok, so what we know is 1 horizontal asymptote y=1 2 vertical asymptotes x= -1 and x=1 2 zeros at x= 2 and x=3

OpenStudy (phi):

can you plot those lines and/or points ?

OpenStudy (phi):

it looks like this

OpenStudy (phi):

now we need to fill in the curve.

OpenStudy (dobby1):

yeah but how do we do that

OpenStudy (phi):

First, we now the curve is near y=1 when x is big. Let's figure out where it is when x is a large negative number if we pick x= -100, and plug that into the equation what do we get for y ?

OpenStudy (phi):

\[ y = \frac{-102 \cdot -103}{-101 \cdot -99} \] it will be about +1.05 (above the line y=1)

OpenStudy (dobby1):

ok. what does that mean?

OpenStudy (dobby1):

I am sorry I am being difficult I have a massive headache and cant be done with school till this is done

OpenStudy (phi):

as you go more and more negative the curve gets closer to 1 (but never reaches it... |dw:1391641347940:dw|

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