# Chapter 1 - Section 1.2 - Informal Geometry and Measurement - Exercises - Page 19: 43

x = 23

#### Work Step by Step

tep 1: m$\angle$ 1 + m$\angle$ 2 = m$\angle$ ABC. Step 2: Substitute x for m$\angle$ 1, (2x + 3) for m$\angle$ 2, and 72 for m$\angle$ ABC. x + (2x + 3) = 72 Step 3: Simplify the left side of the equation. 3x + 3 = 72 Step 4: Subtract 3 from both sides of the equation. 3x + 3 - 3 = 72 - 3 Step 5: Simplify. 3x = 69 Step 6: Divide both sides by 3. $\frac{3x}{3}$ = $\frac{69}{3}$ Step 7: Solve. x = 23

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