You can put this solution on YOUR website! if you know the measure of the interior angle, then the exterior angle is 180 - it.
the exterior angle is supplementary to its corresponding interior angle.
that means that 180 degrees - interior angle degrees = exterior angle degrees.
if your interior angle is BAC (vertex at A), then take one of the sides (either BA or AC) and extend it past the vertex in a straight line to point D.
if you used line BA, it would be the extended line BD.
if you used line CA, it would be the extended line CD.
you only use one, not both.
you have now formed a new angle.
let's say you extended BA
your new line goes from B straight through A to D.
your new angle is BAD.
that angle is supplementary to BAC since the sum of BAC and BAD is 180 degrees.
the exterior angle is always supplmentary to it's corresponding interior angle.
the exterior angle is always 180 degrees - the interior angle degrees.