An exterior angle is one formed by one side of a triangle and extension of an adjacent side of the triangle.The sum of two non-adjacent interior angles will equal the measure of the exterior angle of the triangle.
In finding the value of ∠BAC first find ∠BCA (180°-113°=67°) ⇒sum of angles formed in a straight line add up to 180°
∠BAC= 180°-(∠ABC +∠BCA)⇒sum of angles in a triangle
