Exercise 11 Page 612

According to the Base Angles Theorem, if two sides of a triangle are congruent, then the angles opposite them are congruent. Therefore, it must be that $x^{\circ} = 7 9^{\circ} .$

According to the Triangle Sum Theorem, the sum of the measures of the interior angles of a triangle is

18 0^{\circ} .

Using this, we can write an equation.

y^{\circ} + 7 9^{\circ} + 7 9^{\circ} = 18 0^{\circ}

Let's solve this equation.

y^{\circ} + 7 9^{\circ} + 7 9^{\circ} = 18 0^{\circ}

AddTerms

Add terms

y^{\circ} + 15 8^{\circ} = 18 0^{\circ}

SubEqn

$LHS - 15 8^{\circ} = RHS - 15 8^{\circ}$

y^{\circ} = 2 2^{\circ}