Exercise 13 Page 616

Let's mark the congruent corresponding parts in our triangles. Note that the naming of the triangles can help us in this regard: △ D E F≅ △ Q R S D and Q are corresponding vertices, as are E and R and F and S.

Examining the triangles, we see that ∠ F and ∠ S are congruent corresponding angles. Thus, to find x we need to know ∠ F. Using the Triangle Sum Theorem, we can write an equation to determine ∠ F: 29^(∘)+123^(∘)+m∠ F=180^(∘) Let's solve this equation.

When we know the measure of ∠ F we can equate this with the measure of ∠ S and solve for x.

To find the value of y, we equate the expression for DE, (5y-7), with it's congruent corresponding side in △ QRS which is known.