silly math equation

Dijos

Dijos

Joined
Nov 20, 2001
Messages
2,600
I should know how to do this , but I am trying to figure out where these two lines intersect:

y=.15(x-7000)+700
and
y=.25(x-28000)+3910

If I had a graphing calculator, I could do it, but I'm trying it by hand, and only getting as far as:
-3210=.15(x-7000)+.25(x-28000)

I think that I have to divide or something, but because the things in parentheses (f of x) are different, My brain is stopping.
 
Dijos said:
If I had a graphing calculator, I could do it, but I'm trying it by hand, and only getting as far as:
-3210=.15(x-7000)+.25(x-28000)

I think that I have to divide or something, but because the things in parentheses (f of x) are different, My brain is stopping.
Click to expand...

Better get your brain moving. You've made a mistake already.

Step 1: Sharpen a pencil.
Step 2: Get a piece of paper.
Step 3: Equate the two: .15(x-7000) + 710 = .25 (x-28000) +3910
Step 4: subtract 710 from each side: .15(x-7000) = .25(x-28000) + 3210
Step 5: multiply out, collect terms, and balance the equation.
Step 6: divide both sides by the x multiplier.

Did you think that you would get off so easy as to having someone solve the equation for you? :D
 
y=.15(x-7000)+700
and
y=.25(x-28000)+3910
Click to expand...
First step: multiply each term within parens by the term preceding parens

.15x - .15 times 7000 + 700
and
.25x - .25 times 28000 + 3910
 
How old are you?

You're not going through it far enough.

You need to think about the 2 lines. Where it intersects is where for both lines the Y and X would be the same. So firstly....

y from 1st line = y from 2nd line
0.15(x-7000)+700=0.25(x-28000)+3910

then you just complete the whole thing
in other words multiply and add and subtract whatever

0.15x-(0.15)(7000)+700=0.25x-(0.25)(28000)+3910

then you bring all of them together

0.25x-0.15x=(0.25)(28000)-(0.15)(7000)-3910+700

Then...

x=[(0.25)(28000)-(0.15)(7000)-3910+700]/(0.25-0.15)

Put that all in your calculator and you get the x-intersect.
Put that in one of the line equations and you get y-intersect.

It's been a long time since i did this. Probably close to 10 years since i first learned it so i'm not 100% sure

EDITED: Made a big boo boo, LEFT out a 700 somewhere in the equation. Now it's correct.
 
I went through it, and got x=27400. when I put it back into the eqation, the sides didn't balance out..does this mean that the lines don't intersect? BTW, I'm 30...sad.
 
Don't worry you are not stupid, you are only careless.....if that makes you feel better :D.

The answer I got, running it down real quick was 28400.

Btw.: When you meantioned a graphing calculator, you nearly destroyed any sympathetic feelings I had. The numbers are so nice that you can easily do all of it in you head, though a pencil and paper helps.
 
Graphing calculator ... ha ha ha ha ha ha ha ... we used slide rules. It was about ten years after I got out of high school that electronic calculators showed up in the marketplace.
 
The you see, I have to eat my own words....again. I am the careless one: it is 27400. Just did it a bit slower again. Oooops. :rolleyes:
 
If you think it out clearly, almost all lines will intersect somewhere UNLESS they are perfectly parallel to each other.

In this equation if you got a perfect number like x=27400 (which i got as well), then YOU MUST HAVE an intersect since you've already proven that:

y from 1st line=y from 2nd line (WHEN x=27400)

So all you need to put in is x in one of the line equations. You will get something like y=3760. IT MUST BE THE SAME FOR BOTH LINES. You can check it with both equations if you want to but that's not really necessary since you already equated the equations in the first step.

So the lines intersect at x=27400 and y=3760

Oh the joy of mathematics. I miss it sometimes. BTW i do use a graphing calculator but rarely use the graphing functions. Used to use it a bit but didn't really find it all that useful if you already know the functions. In this case it would be difficult to show since the intersect is so far away. You don't need one for this equation anyway. However, what i do like about my Sharp calculator is its equation editor. VEry useful feature. What you can do is write up all the long equations without calculating between steps and just plonk it down in the calculator in the last step. It even has division functions that look like division instead of using a slash (/). So you get equations on top of each other which is easier on the eye and avoids careless mistakes.

Quote from SHarp website:

"Sharp was the first to introduce a technology called Advanced Direct Algebraic Logic. D.A.L. is an innovation which allows students to enter the elements of an equation into a calculator in the exact order they appear in the textbook."

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Damn this should be in gadgets and gear. It's just that i've been using the same sharp calculator for almost 8 years now and it's saved my butt a few times due to the equation editor. During my degree course finals i had like 5 minutes left for the last question which was kind of a big question you're supposed to do in 20-30 minutes but because i could leave the calculation to the end all i needed to do was write down one long equation so the lecturer could see the method and just the answer underneath. Aced that exam because of that.
 
Don't let numbers confuse you, it's simple:

y=a(x-b)+c

y=d(x-e)+f

...

x = (ab-de-c+f) / (a-d)

---------------------------------

I still have my old ones, this one is from my High school days.

Luis

e188t1.jpg
 
Since they are both equal to "y" just set them equal to each other and solve for the "x-value". Then substitute that value into one of the equations to find the y- value.
 
Ok, now the booby prize for anybody who knows what the above formulas regard. It is a real life equation, can anybody recognize it?
 
Burchtree said:
clearly, the answer is "dairy cow." Jeez......

:D
Click to expand...


No the answer is


*Pic Removed*

This is your only warning. Posting inappropriate pics outside of W&C and Pirates Cove is consideration for getting banned. Do not do it again.

K.V. Collucci
 
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