Question

please solve this question

Answer 1

ABCDE is a regular Pentagon :

AB=BC=CD=DE=EA

Angle DEB = x

In ΔBDE,
∠b + ∠c + ∠x = 180° [Angle sum property of triangle] →(1)
Also each angle of a regular pentagon is 108°
Hence ∠a + ∠x = 108°
⇒ ∠x = 108° – ∠a
∴ Equation (1) becomes,
∠b + ∠c + 108° – ∠a  = 180°
⇒ ∠b + ∠c – ∠a  = 180° – 108° = 72°