pentagon angles

the three angles at each corner (vertex) seem to be equal
are they?

by symmetry the angles in  the yellow triangles must be the same

how can you show that the angle in the blue triangle (b) also = a?

write down an equation involving 'a' and 'b' for the yellow triangle

write down an equation involving 'a' and 'b' for this brownish triangle

use these two equations (solve them) to show that a = b