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avatar+8262 

I don't understand why the answer is is listed like that below. In the homework, the answer is $$\frac{b-7}{a^3}$$

Please help. I don't want to register, so please help. Thank you.

Question:

$$\dfrac{a^2b-7a^2}{a^5}$$

Possible answers:

$$\boxed{\dfrac{b-7}{a^3}},\mbox{\;or\;}\boxed{a^2b-\dfrac{7}{a^3}}$$

 Sep 24, 2014

Best Answer 

 #1
avatar+129899 
+13

Note, DS, that we have the law of exponents that says  an / am   = a n-m

So.....look at the fraction....we have

7 * ( a2 / a5)     and using this law, we have

7 * (a 2-5 )  =   7 * a-3

And remember that  a-n   = 1 / an

So.......

7 * a-3  =   7 * ( 1 / a3)  = (7 / a3 )

So...our answer should be

a2b - (7/a3)     

Does that help ???

 

 Sep 24, 2014
 #1
avatar+129899 
+13
Best Answer

Note, DS, that we have the law of exponents that says  an / am   = a n-m

So.....look at the fraction....we have

7 * ( a2 / a5)     and using this law, we have

7 * (a 2-5 )  =   7 * a-3

And remember that  a-n   = 1 / an

So.......

7 * a-3  =   7 * ( 1 / a3)  = (7 / a3 )

So...our answer should be

a2b - (7/a3)     

Does that help ???

 

CPhill Sep 24, 2014
 #2
avatar+8262 
0

It does, but it is confusing. And the answer is not there in the homework. I will shoot the photo, and you would see that the answer isn't there, and it will be my proof and evidence that the answer is not there. So, do I shoot the photo?

 Sep 24, 2014
 #3
avatar+129899 
+5

Isn't my answer the same thing as your second "possible" answer ???

 

I'm confused !!!    ????????

 Sep 24, 2014
 #4
avatar+8262 
0

Yes it is. And it is incorrect, I guess. I will shoot the photo.

 Sep 24, 2014
 #5
avatar+8262 
0

Only help on T.

 Sep 25, 2014
 #6
avatar+8262 
0

I may need help on the ones of subtracting. Can you teach me how to do it?

 Sep 25, 2014
 #7
avatar+129899 
+8

OK.....if we have

[a2b - 7a2] / a5       we can factor out an a2  at the top and we have

[(a2) (b - 7)] / a5   =

[b - 7 ] / a

 

 Sep 25, 2014
 #8
avatar+8262 
0

I have a question. In the first step, why do you cancel out $$a^2?$$

 Sep 25, 2014
 #9
avatar+118687 
+5

Hi Dragon  

 

$$a^2b-7\frac{a^2}{a^5}\\\\
a^2b-\frac{7}{1}\times\frac{a^2}{a^5}\\\\
a^2b-\frac{7\times a^2}{1\times a^5}\\\\
a^2b-\frac{7a^2}{a^5}\\\\
a^2b-\frac{7aa}{aaaaa}\\\\
a^2b-\frac{7\not{a}\not{a}}{\not{a}\not{a}aaa}\qquad \mbox{Note: aa cancels out}\\\\
a^2b-\frac{7}{aaa}\\\\
a^2b-\frac{7}{a^3}\\\\$$

 Sep 25, 2014
 #10
avatar+8262 
0

I am more confused.

 Sep 25, 2014
 #11
avatar+118687 
+8

Dragon, you wrote that before you even had time to think about what I had written!!!

 

Now go back and think about it properly!

 Sep 25, 2014
 #12
avatar+8262 
0

May someone explain how you canceled out aa???

 

And can someone help me figure out to do in the following problem please?:

$$\dfrac{6a^2-30a+36}{4a-12}$$ 

How do I start off, and can you give an example of how to do it?

 Sep 25, 2014
 #13
avatar+238 
+8

=6(a^2-5a+6)/4(a-3)=6(a-2)(a-3)/4(a-3)=3/2*(a-2)=3*a/2-3

 Sep 25, 2014
 #14
avatar+8262 
0

Melody, you're answer is not on the sheet.

 Sep 25, 2014
 #15
avatar+118687 
+5

It was your very fist MathWay question!  the answer had a blue tick!

 Sep 25, 2014
 #16
avatar+129899 
+5

[ 6a2 -30a + 36 ] / [4a - 12 ]   factor out the common factor of 6 at the top and 4 at the bottom

(6/4) [a2 - 5a + 6 ] / [a - 3]   factoring the trinomial, we have

(6/4) [(a -3)(a-2)] / (a-3)      "canceling the "(a-3)'s "  and reducing (6/4) we have

(3/2)(a - 2) or   (3a - 6) / 2    ...whichever you prefer !!!

 

 Sep 25, 2014
 #17
avatar+8262 
0

Oh! I get the answer now! Melody, how do you know it is my first MathWay question? This is my third, but I didn't post it here...

 Sep 25, 2014
 #18
avatar+8262 
0

Can you guys help on the following?

$$\dfrac{3a^3(16-a^2)}{12a^6(a^2-9a+20)}$$

I got to the part:

$$\dfrac{1(16-aa)}{4a^3(a^2-9a+20)}$$ 

I don't know what to do next. Can you pleas tell me what to do next?

 Sep 25, 2014
 #19
avatar+8262 
0

May anyone help me here!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!??!?!?!??!!?!

 Sep 25, 2014
 #20
avatar+129899 
+8

3a3(16- a2) / [12a6 (a2 - 9a + 20)]   factoring everything, we have

 

3a3 (4 - a)(4+a) /[ 12a6 (a - 4)(a-5)] =

-(1/4a3 )(a-4)(a+4)/[(a-4)(a-5)] =   (we can factor a "-" out of (4 - a) = - (a - 4))

-(1/4a3)(a+4)/(a-5) = (5-a)(4+a)/(4a3)

 

 

 

 Sep 25, 2014
 #21
avatar+8262 
+8

Thank you! I need to understand what to do for other similar questions like that one. Can you please tell or explain what to do in questions like these?

thanks. I would give you hundreds and hundreds of points CPhill.

 Sep 25, 2014
 #22
avatar+129899 
+5

I don't have any "magic" formula for doing these, DS......it's mainly just factoring and "cancelling"......plus a few algebraic "tricks".......

 

 Sep 25, 2014
 #23
avatar+118687 
+5

Much of this is WAY OVER your head Dragon.  Your teacher cannot seriously expect you to do it!!

 Sep 25, 2014
 #24
avatar+8262 
0

I know. The teacher said, " try your best. I will tell you how on Friday" 

so, I try to make the best work I can. Ok. I know. It is not my level, but thanks for helping.

 Sep 25, 2014
 #25
avatar+118687 
+5

you are welcome Dragon 

 Sep 25, 2014

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