Exercise 13 Page 348

The order of the vertices in the given congruence statement tells us which vertices correspond in the polygons. Let's use colors to illustrate this. B C DE ≅ R S TU

By the order of the vertices in the names of the polygons, we can tell which angles are corresponding angles.

In congruent polygons the corresponding angles are congruent, so they have the same measure. This allows us to set up and solve an equation for x.

m∠ B=m∠ R

SubstituteII

m∠ B= 2x+9, m∠ R= 49

2x+9= 49

SubEqn

LHS-9=RHS-9

2x=40

DivEqn

.LHS /2.=.RHS /2.

x=20