Answer:
Step-by-step explanation:
From the picture attached,
a). Triangle in the figure is ΔBCF
b). Since, and
are the parallel lines and m is a transversal line,
m∠FBC = m∠BFG [Alternate interior angles]
Since, and
are the parallel lines and n is a transversal line,
m∠BCF = m∠CFE [Alternate interior angles]
By triangle sum theorem in ΔBCF
m∠FBC + m∠BCF + m∠BFC = 180°
From the properties given above,
m∠BFG + m∠CFE + m∠BFC = 180°
m∠GFE = 180°
Therefore, angle GFE is the straight angle that will be useful in proving that the sum of the measures of the interior angles of the triangle is 180°.