I'm trying to calculate some steps or stages for a graph and am having
trouble, basically I'm trying to calculate a line between a point x,y
to a point on a line between x1,y1 and x2,y2 that looks some like
this:

.x2,y2(8,6)
/
/-----------------------------------x,y(13,3)
/
.x1,y1(1,1)

I think I got the slope 5/7=0.7142857, but I'm looking for the
equation to calculate line between a point x,y to a point on a line
between x1,y1 and x2,y.

Go easy on me, I haven't been to school in 35 years.

On Jul 2, 4:30*am, Curbie <jim.richard...@yahoo.com> wrote:
> I'm trying to calculate some steps or stages for a graph and am having
> trouble, basically I'm trying to calculate a line between a point x,y
> to a point on a line between x1,y1 and x2,y2 that looks some like
> this:
>
> * * * * * .x2,y2(8,6)
> * * * * */
> * * * * /-----------------------------------x,y(13,3)
> * * * /
> * * *.x1,y1(1,1)
>
> I think I got the slope 5/7=0.7142857, but I'm looking for the
> equation to calculate line between a point x,y to a point on a line
> between x1,y1 and x2,y.
>
> Go easy on me, I haven't been to school in 35 years.

Start from slope = (y - y1)/(x - x1) = (y2 - y1)/(x2 - x1). From this
we get the equation you want -

y = y1 + (x - x1)*(y2 - y1)/(x2 - x1). In the above case, the
equation is
y = 1 + (x - 1)*(6 - 1)/(8 - 1) or. if you really need to simplify
this y = 2/7 + 5/7*x

xt

On 01/07/2011 17:30, Curbie wrote:
> I'm trying to calculate some steps or stages for a graph and am having
> trouble, basically I'm trying to calculate a line between a point x,y
> to a point on a line between x1,y1 and x2,y2 that looks some like
> this:
>
> .x2,y2(8,6)
> /
> /-----------------------------------x,y(13,3)
> /
> .x1,y1(1,1)
>
> I think I got the slope 5/7=0.7142857, but I'm looking for the
> equation to calculate line between a point x,y to a point on a line
> between x1,y1 and x2,y.
>
> Go easy on me, I haven't been to school in 35 years.
>

If you mean to a point half way between x1,y1 and x2,y2, that point is
at (x1+x2)/2, (y1+y2)/2, or at 4.5, 3.5.

If, on the other hand, you mean your line to be horizontal, i.e. y=3,
then your point would have an x value of x1+(x2-x1)*y/(y2-y1), or 1+7*3/5.

David Biddulph

On 06/07/2011 08:48, David Biddulph wrote:
> On 01/07/2011 17:30, Curbie wrote:
>> I'm trying to calculate some steps or stages for a graph and am having
>> trouble, basically I'm trying to calculate a line between a point x,y
>> to a point on a line between x1,y1 and x2,y2 that looks some like
>> this:
>>
>> .x2,y2(8,6)
>> /
>> /-----------------------------------x,y(13,3)
>> /
>> .x1,y1(1,1)
>>
>> I think I got the slope 5/7=0.7142857, but I'm looking for the
>> equation to calculate line between a point x,y to a point on a line
>> between x1,y1 and x2,y.
>>
>> Go easy on me, I haven't been to school in 35 years.
>>
>
> If you mean to a point half way between x1,y1 and x2,y2, that point is
> at (x1+x2)/2, (y1+y2)/2, or at 4.5, 3.5.
>
> If, on the other hand, you mean your line to be horizontal, i.e. y=3,
> then your point would have an x value of x1+(x2-x1)*y/(y2-y1), or 1+7*3/5.
>
> David Biddulph

Correction:
.... x1+(x2-x1)*(y-y1)/(y2-y1), or 1+7*2/5.

David Biddulph