Each equilateral triangle is called an isosceles triangle.

Let's place the set squares on the exercise book and trace two triangles with them. Let's then measure their angles.

                                               Set square No. $1$ gives a $△ABC$                                  Set square No. $2$ gives a $△PQR$

Measured with protractor, $\angle ABC$ of $△ABC=45°$

Measured with protractor, $\angle ACB$ of $△ABC=$ _____

Measured with protractor, $\angle BAC$ of $△ABC=90°$

In the same way, by using the protractor, the angles of the $△PQR$ are found to be _____, _____ and _____. [Let's do]

                                     $\angle DEF=45°$                                                                  $\angle GHI=60°$

Let's measure the angles with protractor and verify.

                                     $\angle DEF=45°$                                                          $\angle GHI=60°$

Using set square, let us draw $90°$ angle and verify with protractor.

         $\angle MNO=45°+30°=75°$                                         $\angle PQR=60°+45°=105°$

Let's try to draw $120°, 135°, 150°$ angle using set squares.

Using Set square, let us draw $\overleftrightarrow{AB}\parallel \overleftrightarrow{CD}\parallel \overleftrightarrow{EF}$.