Let the number of sides be n and use the formula: 1/2n(n-3) = diagonals
1/2n(n-3) = 27
Multiply both sides by 2 and then form a quadratic equation:
n2-3n-54 = 0
Solving the above quadratic equation works out as:
n = -6 or n = 9 it must be the latter because the sides can't be negative
Therefore the polygon has 9 sides.
its called regular nanogon where nano means 9.