## Elementary Geometry for College Students (6th Edition)

m$\angle$A=108^{\circ}
By the same proof as the previous problem, angles 1 and 3 are congruent. m$\angle$1=m$\angle$3=36$^{\circ}$ m$\angle$A+m$\angle$1+m$\angle$3=180 m$\angle$A+36+36=180 m$\angle$A=108$^{\circ}$