Răspuns :
∡(DFE) = 180°-140° =40° grade
∡( D - E) =20 ⇒∡ D =20° +∡E
∡(F+D +E )=180°
40°+ (20°+∡E )+∡E =180°
60° +2∡ E =180°
2∡E =180° -60°
2∡E =120°
∡E =60°
∡D =20°+∡E=20 °+60 °=80 °
∡D=80°, ∡E=60°, ∡F=40°
∡( D - E) =20 ⇒∡ D =20° +∡E
∡(F+D +E )=180°
40°+ (20°+∡E )+∡E =180°
60° +2∡ E =180°
2∡E =180° -60°
2∡E =120°
∡E =60°
∡D =20°+∡E=20 °+60 °=80 °
∡D=80°, ∡E=60°, ∡F=40°