denise9423
Can someone plz help me get started on these fractions
f(x)=3x-8 div 4x+20
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AsianDuck
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What do you need?
saifoo.khan
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\[\frac{ 3x - 8}{4x + 20}\to \frac{3x-8}{4(x+5)}\]As there is nothing common between denominator and numerator so we cannot simply it.
denise9423
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sorry I just found this.
saifoo.khan
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No worries! :D
denise9423
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How do I find the domain
denise9423
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hi
Akshay_Budhkar
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domain is all real numbers except for -5
brinethery
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No division by zero. So what is x going to be when the denominator is zero?
denise9423
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saifoo.khan
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set the denominator equal to zero right? @Akshay_Budhkar
brinethery
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no. x cannot = -5.
Akshay_Budhkar
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Yes @sai
Akshay_Budhkar
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@saifoo.khan
denise9423
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f(x)=3x-8 over 4x+20
brinethery
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@denise9423 Domain means all of the values x can take on.
Here's your domain:
\[x \neq-5\]
Akshay_Budhkar
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If you have a look the function is having real values for all values except for x=5 when it is not defined as the denominator is zero
denise9423
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can you show me how to get 5
brinethery
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4x+20 =0
Solve for x.
x=-5.
brinethery
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Do you know why division by zero is not allowed?
denise9423
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ok,then can i sub it also 3x-8
brinethery
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no!
brinethery
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you only need to worry about the bottom.
denise9423
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no to ur question
ok
brinethery
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Remember this: What is 1 divided by 0? In other words, what times zero can equal 1? 0*2? 0*3? There is nothing you can multiply by zero to get 1.
So whenever you get these fractions and they ask you to find the domain, just think about what x has to be in order for the denominator to equal zero.
brinethery
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If you have an equation in the denominator, then set that equal to zero :-)
brinethery
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*and solve for x.
denise9423
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like this 4x+20=0
brinethery
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Yup! :-)
denise9423
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ok
brinethery
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Or if you have 1/(x^2+2x+3) . If you have something weird like that, then set it equal to zero and use the quadratic formula to solve for your two x-values. Those x-values are what x can't equal. Sorry, I sound like I'm talking in riddles lol.
denise9423
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ok so -7xyy over 28xxxxxy=0
brinethery
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Are you in algebra?
denise9423
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yes and Its rough
brinethery
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I'm gonna be more specific with what I said, sorry my fault:
Or if you have 1/(x^2+2x+3) . If you have something weird like that, then set it equal to zero and use the quadratic formula to solve for your two x-values. Those x-values are what x can't equal. Sorry, I sound like I'm talking in riddles lol.
x^2+2x+3 = 0 (then use the quadratic formula and solve for x)
brinethery
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That's okay!
brinethery
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I don't think they'll ask you to find the domain of something with x's and y's. Or are they?
denise9423
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yes
denise9423
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no sorry
denise9423
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simplify
brinethery
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I can help you on something like that, but first off is that denominator stuff making sense? Really sleep on that and try to remember it b/c it's super important for calculus.
denise9423
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-7xyy/28xxxxxy
brinethery
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Okay well what multiples to 7 and 8 have in common? What can you divide them both by?
brinethery
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I mean 28.
denise9423
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yes it does bc it will help me remember to put=0 so I can solve for x
brinethery
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good :-)
denise9423
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brinethery
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-7xyy/28xxxxxy
You can divide the numerator and denominator by 7.
Also, which has the smallest amount of x's, and then which one has the smallest amount of y's?
denise9423
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3x7=28
denise9423
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no 4x7=28
brinethery
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The numerator has the smallest amount of x's. There is 1 of them. The denominator has the smallest amount of y's, which is 1 y.
So we'll divide the numerator and denominator by 7.
-1*x*y*y/4xxxxxy
denise9423
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bottom has 5 x's and the top has 2 y's
brinethery
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We have to cancel out the smallest amount of x's. And we also cancel out the smallest amount of y's.
So we have: -1*y/4xxxx
I canceled out an x on the top and bottom. Then I canceled out a y on the top and bottom.
denise9423
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ok
denise9423
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sorry i have a 911 gotta chk out b back later thank you for all ur help god bless
brinethery
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k