Given the points (1,2) and (3,4), calculate the distance from (0,0) to the line that passes through the points (1,2) and (3,4).

The equation of the line joining (x1, y1) and (x2,y2) 
is:

y-y1 = (y2-y1)/(x2-x1) .  Given (x1,y1)  = (1,2) and
(x2,y2) = (3,4).

So the equation of the line  joining (1,2)
(3,4) is:

y-2 = (4-2)/((3-1)
{x-1}

y-2 = (x-1)

0 =
x-y-1+2

x-y+1 =
0.....................(1)

The distance d of the  the point
(x1, y1) from the line ax+bx+c is given by:

d = |
|(ax1+by1+c)/sqrt(a^2+b^2)|

 Therefore , the distance d of 
(0 , 0 ) from the line at (1) is:

d |(
1*00-1*0+1)/sqrt[1^2+(-1)^2] = 1/sqrt2.