In the triangle LME, the sum of the angles equals 180°.
Thus angle LUM = angle ULM = 65°. In the triangle ULM, angle LUM = 180 - (50 + 65) = 65°. As the points U, M and E are aligned, the angle UME measures 180°. Thus angle LME = 180 - ( 25 + 40) = 115° Thus angle UML = 180 - 115 = 65° Thus the triangle ULM has two congruent angles. Thus the triangle ULM is isosceles at U.