Proved that one interior angle of pentagon is three times the exterior angle of decagon.

Explanation

One interior angle of a pentagon `=(n−2)xx 180/n`
where `n=5`
`=(5−2)xx 180/5`
`=108^0`
Exterior angle of any polygon is `360^0`
One exterior angle of decagon `= 360/10`
`=36^0`
`108=3xx36`
Therefore it's proved that one interior angle of pentagon is three times the exterior angle of decagon.