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Offline LRHogfan

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Algebra gurus
« on: March 17, 2010, 02:04:33 PM »
I'm in the position of having to tutor my 13 year old in Algebra.  :-\   I used to be pretty good at this crap, but it's been a llllllooong time.

I understand generally how to solve quadratic equations, but there are some word problems I CAN'T do, like this:

A small rocket is fired from the ground. H(t) = 1/2(-9.8)t^2 + 49t + 2.5 describes the rocket's projectile motion. Approximately how many seconds does it take for the rocket to return to the ground?

I started with this: 0(t) = -4.9t^2 + 49t + 2.5 
I think this needs to be factored in order to come up with two values for t, one of which will be tossed out because it will be negative, but I'm lost.  WTF?

Can anyone show me how to finish this so I can TRY to explain it to my 8th grader?  Please?  ;D


Offline Ahole

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Re: Algebra gurus
« Reply #1 on: March 17, 2010, 02:16:01 PM »
I googled your equation (H(t) = 1/2(-9.8)t^2 + 49t + 2.5) and it gave me the answer in this .pdf. Here's the link:

http://www.lessonlink.com/documents/da2/ParentGuide/DA_PG_09.pdf


Offline Hobo

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Re: Algebra gurus
« Reply #2 on: March 17, 2010, 02:17:00 PM »


Offline jhawg05

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Re: Algebra gurus
« Reply #3 on: March 17, 2010, 02:25:02 PM »
use the quadratic formula to solve for 't'.

x=\frac{-b \pm \sqrt {b^2-4ac}}{2a}, I have no idea what that says; so, i would just google quadratic formula.  You should get 2 quantities.  The starting point and when it hits the ground.  

a=t^2
b=t
c=scaler

« Last Edit: March 17, 2010, 02:31:14 PM by jhawg05 »

Offline LRHogfan

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Re: Algebra gurus
« Reply #4 on: March 17, 2010, 02:34:16 PM »
I googled your equation (H(t) = 1/2(-9.8)t^2 + 49t + 2.5) and it gave me the answer in this .pdf. Here's the link:

http://www.lessonlink.com/documents/da2/ParentGuide/DA_PG_09.pdf

Good grief. I didn't think there would be any way that particular equation would be found. I was googling quadratic equations in general to try to work it out.  :-\

On the sample solution, it says "The zeros are at approximately 0.05 and 10.05" but I don't know how to get there. So there's still a disconnect, at least in my dumbass brain.

I got this...
http://www.addictinggames.com/papercannon.html
You suck.  ;)

use the quadratic formula to solve for 't'.

x=\frac{-b \pm \sqrt {b^2-4ac}}{2a}, I have no idea what that says; so, i would just google quadratic formula.  You should get 2 quantities.  The starting point and when it hits the ground. 

a=t^2
b=t
c=scaler
Let me see if I can make sense of that. Like I said, I've googled and found plenty of general help on equations. It's just these particular word problems I can't figure out.


Offline LRHogfan

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Re: Algebra gurus
« Reply #5 on: March 17, 2010, 02:57:31 PM »
use the quadratic formula to solve for 't'.

x=\frac{-b \pm \sqrt {b^2-4ac}}{2a}, I have no idea what that says; so, i would just google quadratic formula.  You should get 2 quantities.  The starting point and when it hits the ground.  

a=t^2
b=t
c=scaler
Got it. It really was a simply as plugging a, b & c into the formula.  Duh.  ::)

Thanks!


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Re: Algebra gurus
« Reply #6 on: March 17, 2010, 03:42:06 PM »
I'm in the position of having to tutor my 13 year old in Algebra.  :-\   I used to be pretty good at this crap, but it's been a llllllooong time.

I understand generally how to solve quadratic equations, but there are some word problems I CAN'T do, like this:

A small rocket is fired from the ground. H(t) = 1/2(-9.8)t^2 + 49t + 2.5 describes the rocket's projectile motion. Approximately how many seconds does it take for the rocket to return to the ground?

I started with this: 0(t) = -4.9t^2 + 49t + 2.5 
I think this needs to be factored in order to come up with two values for t, one of which will be tossed out because it will be negative, but I'm lost.  WTF?

Can anyone show me how to finish this so I can TRY to explain it to my 8th grader?  Please?  ;D

I took Algebra 1 threve times at the UA and I still have nofaking clue what to do with that mess. How I made it through survey of cal is truly one of life's great mysteries.

No fucks were wasted in the preceding message.

Offline Hobo

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Re: Algebra gurus
« Reply #7 on: March 17, 2010, 04:04:59 PM »


Offline Ahole

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Offline jhawg05

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Re: Algebra gurus
« Reply #9 on: March 17, 2010, 04:33:16 PM »
Got it. It really was a simply as plugging a, b & c into the formula.  Duh.  ::)

Thanks!



There isn't 2 answers as I mentioned.  Obviously a negative number does not fit in the equation for time.  So, their is only one real answer.  Can't have negative time.  Clear as mud?


Offline LRHogfan

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Re: Algebra gurus
« Reply #10 on: March 17, 2010, 04:36:17 PM »
Can't have negative time. 

I consider the time I've spent on this to be VERY negative time.  :D


Offline chop sooie

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Re: Algebra gurus
« Reply #11 on: March 17, 2010, 09:16:50 PM »
I got all the way through AP Calculus in high school. Then I aced college algebra and trig my first year in college. Never had a problem with math at all.

Then I tried to go back 13 years later and take pre-engineering courses, the first math course of which is Calculus 1. I failed miserably.  It ain't like riding a bike.

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Offline shotmaster03

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Re: Algebra gurus
« Reply #12 on: March 17, 2010, 11:45:04 PM »
I got all the way through AP Calculus in high school. Then I aced college algebra and trig my first year in college. Never had a problem with math at all.

Then I tried to go back 13 years later and take pre-engineering courses, the first math course of which is Calculus 1. I failed miserably.  It ain't like riding a bike.

How in the world did you take AP Cal in HS but have to take college algebra and trig in college??? Trig is about 2 years before Cal at the HS level


Offline chop sooie

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Re: Algebra gurus
« Reply #13 on: March 18, 2010, 12:55:36 AM »
How in the world did you take AP Cal in HS but have to take college algebra and trig in college??? Trig is about 2 years before Cal at the HS level

Required college credits for an architecture major. The UA could care less what I took in HS unless I passed the AP exam in Cal, which I didn't take.

« Last Edit: March 18, 2010, 12:59:36 AM by chop sooie »
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Offline Nick Ahpleeze

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Re: Algebra gurus
« Reply #14 on: April 15, 2010, 09:46:44 PM »
I made a B on my college algebra final. Happiest day of my 7 yr on/off college career.

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Re: Algebra gurus
« Reply #15 on: April 29, 2010, 12:08:11 PM »
I made a B on my college algebra final. Happiest day of my 7 yr on/off college career.

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Offline jesus

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Re: Algebra gurus
« Reply #16 on: May 06, 2010, 12:52:02 AM »

I made a B on my college algebra final. Happiest day of my 7 yr on/off college career.



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Offline Cerdo

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Re: Algebra gurus
« Reply #17 on: July 25, 2010, 09:11:56 PM »
I took Algebra 1 threve times at the UA and I still have nofaking clue what to do with that mess. How I made it through survey of cal is truly one of life's great mysteries.

I was one of the dumbasses that had to go in late at night to that Bell Lab to have Asian guys tutor me almost every night to pass Algebra at the U of A.   I bet those guys got laid all the time by some desperate chick. 

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