# Prove that in any triangle,the outer angle at a vertex is equal to the sum of the inner angles at the other two vertices.

now G+U+N = 180

and angle N+X = 180 (linear pair)

now, G+U+N = N + X

now here from both LHS and RHS the angle N will cut off

so, now we were remain of G+U = X ( here G and U is your two interior angle and angle X is your outer angle)

here we proved this