# calculate a point

C

#### Curbie

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.

X

#### Xt

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

D

#### David Biddulph

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

D

#### David Biddulph

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