Exercise 5 Page 391

Let's begin with recalling that a linear pair is a pair of adjacent angles with non-common opposite sides.

Remember that the measures of these two angles always have a sum of $18 0^{\circ}$ as together they create a straight angle. Now, let's look at the given picture.

As we can see,

∠ 3

and

4 3^{\circ}

form a linear pair. Therefore, we can write that the sum of the measures of these angles is equal to

18 0^{\circ} .

m ∠ 3 + 4 3^{\circ} = 18 0^{\circ}

SubEqn

$LHS - 4 3^{\circ} = RHS - 4 3^{\circ}$

m ∠ 3 = 18 0^{\circ} - 4 3^{\circ}

SubTerm

Subtract term

m ∠ 3 = 13 7^{\circ}