Exercise 4 Page 473

Let's begin with recalling the Exterior Angle Theorem. The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles.

Now, let's look at the given picture.

The exterior angle in this triangle is equal to 126^(∘), and the two remote interior angles are 73^(∘) and ∠2. To find m∠2, we will use the fact that the sum of the measures of two remote interior angles are equal to the measure of exterior angle.

m∠2+ 73^(∘)= 126^(∘)

SubEqn

LHS-73^(∘)=RHS-73^(∘)

m∠2=126^(∘)-73^(∘)

SubTerm

Subtract term

m∠2=53^(∘)