Solver Calculate solid angle on a cone

Source code of 'Calculate solid angle on a cone'

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==section input
The solid angle of a cone with apex angle a *[input angle=30] degrees on a unit sphere is.

==section solution
perl
if($angle<0 || $angle>180)
{
print " Please enter the value between 0 and 180 to calculate the solid angle"
}
else{
my $angle1=2*3.14159265*(1-cos($angle/2));
my $angle2=$angle1*2*3.14159265/360;

print " <A HREF=Introduction-to-Solid-angles.lesson>The Solid Angle
</A>

The Solid angle for a cone of apex angle A on a unit sphere is,
{{{Solid Angle=(2*pi*(1-cos(A/2)))}}}

{{{Solid Angle=(2*3.14159265*(1-cos($angle/2)))=$angle1}}} degrees

Conversion of angles from <b><A HREF=Degree_%28angle%29.wikipedia>degrees</A></b> to <b><A HREF=Radian.wikipedia>radian</A></b>:
The relation between two units of angle measurement is :
 
2*{{{pi}}} rad = 360 degrees

The Solid angle in radians is,
{{{Solid Angle=(2*pi*(1-cos(A*pi/360)))}}}

{{{Solid Angle=(2*pi*(1-cos($angle*pi/360)))=$angle2}}} radians

Hence, The Solid angle is $angle1 degrees and $angle2 radians.

";
}

==section output
angle1,

==section check
 angle=60 angle2=0.84178721