## Elementary Geometry for College Students (7th Edition) Clone

$m∠A=m\angle C =69^{\circ}$
we know sum of all three angles of triangle is $180^{\circ}$ $m∠A+m∠B+m∠C$=$180^{\circ}$ $m\angle A+42^{\circ}+m\angle C$ = $180^{\circ}$ $m∠A+m\angle C$= $180^{\circ}−42^{\circ}$ $m∠A+m\angle C$ = $138^{\circ}$ $m∠A=m\angle C= 138^{\circ}\div2 =69^{\circ}$