## Elementary Geometry for College Students (5th Edition)

$∠A = 59^{\circ}$
we know sum of all three angles of triangle is 180∘ $m∠A+m∠B+m∠C= 180^{\circ}$ $m\angle A+39^{\circ}+82^{\circ} =180^{\circ}$ $m\angle A+121^{\circ} =180^{\circ}$ $∠A = 180^{\circ}−121^{\circ}$ $∠A = 59^{\circ}$