Solver Addition of signed numbers

Source code of 'Addition of signed numbers'

This Solver (Addition of signed numbers) was created by by ichudov(507)

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==section input
This is the <B>addition</B> solver. There is also a separate 
<A HREF=subtraction-of-signed-numbers.solver>subtraction</A> solver.

Calculate and explain: *[input a=4] <FONT SIZE=+3 COLOR=red>+</FONT> *[input b=-2].

==section solution
perl

$sum = $a+$b;
if( $b < 0 ) {
  print "$b is a negative number. As you know, addition of a negative number is equivalent to SUBTRACTION of its opposite (positive number). In our case, adding $b is equivalent to SUBTRACTING " . (-$b) . ".

{{{$a+ $b = $a-" . (-$b) . "}}}

The difference between $a and " . (-$b) . " is $sum. That's your answer.\n\n\n";
} else {
  print "In this instance, since $b is a positive number, we simply need to perform the addition operation.

$a+$b = $sum.";

}

my $minx = -10;
$minx = $a   if $a   < $minx;
$minx = $b   if $b   < $minx;
$minx = $sum if $sum < $minx;
$minx--;

my $maxx = 10;
$maxx = $a   if $a   > $maxx;
$maxx = $b   if $b   > $maxx;
$maxx = $sum if $sum > $maxx;
$maxx++;

print "{{{
number_line( 400, $minx, $maxx, $a, $b, $sum )
}}}";

==section output
sum

==section check
  a=5 b=-3 sum=2