1) Angle L = angle J : Given 2) Line KJ || line LM: Given 3) angle KML = KMJ: They are alternate interior angles 4) 180 - angle L - angle KLM = angle LKM 180 - angle J - angle KJM = angle JMK 5) because you know two angles of triangle, you know the third. Because angle L = angle J and angle KLM = angle angle KJM, then the remaining angle LKM must equal the remaining angle JMK
