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

m$\angle$ 1 = 120$^{\circ}$
Step 1. m$\angle$ 1 + m$\angle$ 2 = 180$^{\circ}$ Step 2: Substitute in 2x for m$\angle$ 1 and x for m$\angle$ 2. 2x + x = 180 Step 3: Simplify the left side of the equation. 3x = 180 Step 4: Divide both sides of the equation by 3. $\frac{3x}{3}$ = $\frac{180}{3}$ Step 5: Solve. x = 60 Step 6: Substitute the value of x into m$\angle$ 1 = 2x m$\angle$ 1 = 2(60) Step 5: Simplify. m$\angle$ 1 = 120$^{\circ}$