Solver FIND EQUATION of straight line given 2 points

Source code of 'FIND EQUATION of straight line given 2 points'

This Solver (FIND EQUATION of straight line given 2 points) was created by by ichudov(507)

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==section input
Find the equation of line going through points 
(*[input x1=1], *[input y1=2])  and (*[input x2=0], *[input y2=1]).
==section solution
perl

$slope = 0;

print "haha";

if( $x1 == $x2 ) {
  print "Error, the x coordinates of both points are the same. That cannot describe a non-vertical line. Please enter different x values.";
  return undef;
} else {
  $slope = ($y2-$y1)/($x2-$x1);
  $intercept = $y1-$slope*$x1;
  print "We are trying to find equation of form y=ax+b, where a is slope, and b is intercept, which passes through points (x1, y1) = ($x1, $y1) and (x2, y2) = ($x2, $y2).
Slope a is {{{a = (y[2]-y[1])/(x[2]-x[1]) = ($y2-$y1)/($x2-$x1) = $slope}}}.
Intercept is found from equation {{{a*x[1]+b = y[1]}}}, or {{{$slope*$x1 +b = $intercept}}}. From that, 
intercept b is {{{b=y[1]-a*x[1]}}}, or {{{b=$y1-$slope*$x1 = $intercept}}}.

y=($slope)x + ($intercept)

Your graph:

{{{
drawing( 500, 500, -10, 10, -10, 10,
  graph( 500, 500, -10, 10, -10, 10, $slope*x+$intercept ),
  red( locate( $x1, $y1, \"$x1, $y1\" ), circle( $x1, $y1, 0.15 ) ),
  green( locate( $x2, $y2, \"$x2, $y2\" ), circle( $x2, $y2, 0.15 ) )
)
}}}
";
}

==section output
slope
intercept

==section check
  x1=1 y1=1 x2=2 y2=3 slope=2 intercept=-1

==section practice
perl
  $x1 = randint( -5, 2 );
  $y1 = randint( -5, 5 );
  $x2 = $x1+randint( 1, 5 );
  $y2 = $y1 + ($x2-$x1)*randint( -3, 3 );