Math Is Fun Forum

No_Smart

Member

Registered: 2012-06-21

Posts: 5

Problem solving for intersection point

Hi,

I am making a mistake while solving for intersection points of 2 lines :

There is Line L1 from A(512,0) to B(505,5). Another line L2 from C(505,0) to D(507,6)

So, Slope for, L1 = -7/5, L2 = 2/6

To get their intersection points i solve their equations :

Eq. L1 : y = -7/5x + 3584/5 (with point A)

Eq. L2 : y = 2/6 x - 1010/6 (with point C)

So, solving eq. gives me :

-7/5x + 3584/5 = 2/6 x - 1010/6

-42 x + 21504 = 10 x - 5050

52 x = 26554

x = 510.6

But, this is wrong answer (intersection point has to be between 505-507). I dont understand, where i am going wrong. I will be using the suggested method in Excel for futher calculations.

Thanks,
No Smart.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Problem solving for intersection point

Hi No_Smart;

Your equations are not correct. I use the pointpoint formula.

Plugging in the points:

I am getting:

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Problem solving for intersection point

Your line equations aren't correct. How did you get 3584/5 and -1010/6 ?

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
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No_Smart

Member

Registered: 2012-06-21

Posts: 5

Re: Problem solving for intersection point

Hi anonimnystefy,

taking (y-y1) = m (x-x1) (m is slope)

for L1 : (y-0) = -7/5 (x-512)......A co-ordinates (512,0)

y = -7/5 x + 3584/5 ......

L2 : (y-0) = 2/6 (x-505).........C co-ordinates (505,0)

y = 2/6 x - 1010/6 .........

am I wrong ?

Last edited by No_Smart (2012-06-24 05:02:53)

No_Smart

Member

Registered: 2012-06-21

Posts: 5

Re: Problem solving for intersection point

Hi bobby, got it, will try it in excel. thx. But still thinking what was wrong in my previous method.

Thanks

Last edited by No_Smart (2012-06-24 05:05:04)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Problem solving for intersection point

Hi;

Try to be a bit more careful and it will work out fine.

for L1 : (y-0) = -7/5 (x-512)......A co-ordinates (512,0)

You figured the slope wrong. It is -5 / 7.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.