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How long does it take the giraffe to weigh 85 kg?

  • Thread starter Paulo2014
  • Start date
  • #1
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1. Homework Statement
The weight, W kg, of a giraffe over its first two years of life, is given by the equation
W=(t^2)/4-t+68
where t is the time in months since the giraffe was born.
How long does it take the giraffe to weigh 85 kg?

2. Homework Equations



3. The Attempt at a Solution


I know i need to rearage the equation but i cant remember how so any help is appreciated...
 
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Answers and Replies

  • #2
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Which letter represents the weight? Put 85 there and solve it.
 
  • #3
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Yeah I understand that but how would I solve it?

its the (t^2)/4 bit i don't understand how to solve...
 
  • #4
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Let me see if this is the thing you have:
[tex]\frac{t^2}{4}-t+68=85[/tex]
That's a quadratic equation. Before you can solve, what does the equation have to look like?
Then, since fractions give me a headache, like like to ditch them. Can you think of a method of getting rid of them?
 
  • #5
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multiply 4 to both sides?
 
  • #6
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Yes please.
 
  • #7
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So it would be:
t^2-t+68=340?
 
  • #8
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so you have:
[tex]4(\frac{t^2}{4}-t+68=85)[/tex]
make sure that you are careful about your distributive property.
EVERYTHING gets multiplied by 4.
 
  • #9
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but doesn't the t^2 already have the /4 so wouldn't it be:

t^2+4(-t+68=85)?
 
  • #10
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yes
[tex]4(\frac{t^2}{4}-t+68=85)[/tex]
[tex]t^2-(4)t+(4)68=(4)85[/tex]
then what?
 
  • #11
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expand.

So it is t^2-4t+272=340

Is that right?
 
  • #12
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yes.
In order to solve ANY equation, what does it have to be set equal to?
There's ONE MORE STEP before you can solve it.
 
  • #13
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I can't remember... :(
 
  • #14
1,750
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Look for an example in your book.
 
  • #15
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It has to be in the form ax=b

thats what my textbook says.... is that what you meant?
 
  • #16
308
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You are looking for the ZEROS
What would you set the equation equal to to get the ZEROS?
 
  • #17
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i'm lost....
 
  • #18
308
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In order to solve any equation, it must be set equal to ZERO!
HOORAY!
How do you manipulate your equation to get it equal to zero?
 
  • #19
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I see. take 340 from both sides so the equation is:t^2-4t-68=0 is that correct?
 
  • #20
1,750
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Sit down and read the chapter ... do every single example problem!!! It will serve you better than trying to solve this problem.
 
  • #21
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rocomath is right.
and you did get the equation right. If you aren't sure how to solve it, you DO need to read the chapter.
 
  • #22
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I use the quadratic formula don't I...
 
  • #23
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yes you do
 
  • #24
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I got x=10.48528137423857 or -6.4852813742385695
 
  • #25
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Is that right?
 

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