A simple Line question  TOPIC_SOLVED

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A simple Line question

Postby Mason on Mon Jan 26, 2009 2:16 am

Rani is comparing the monthly costs from two internet service providers. #1 charges $10 initially + $.75 per hour #2 is $5 initially and $1 per hour!

How would i figure when the two lines which i already have in y=mx+b which are y=.75x+10 and y=1x+5. how do i figure out the coordinates without using a graph so algebraicly
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Re: A simple Line question

Postby DAiv on Mon Jan 26, 2009 10:03 am

I presume you mean, when do the two lines cross (when do both equations have the same x and y values).

To solve it algebraically, set the first equation equal to the second equation (substitute '.75x + 10' into the y of 'y = x + 5') and solve for x. Then substitute x back into either of the equations to find out y.


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Re: A simple Line question  TOPIC_SOLVED

Postby little_dragon on Mon Jan 26, 2009 1:24 pm

I did this a chapter or two ago. The graphing is so long and boring! Algebraically is faster and easier! Since you have both as "y=", you can just do the two other sides equal to each other: 0.75x + 10 = x + 5. Then minus 0.75 from each side and minus 5 from each side: 5 = 0.25x. 0.25 = 1/4, so times by 4: 20 = x.

You can put 5 in for x in either one of the first equations, and this will give you y. :wave:
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