Properties, Characteristics and proofs: Finding the size of angles in a triangle

Look at the square below:

What is the sum of the angles in the square?

According to the properties of the square, all angles are right angles.

Since there are 4 angles that are all equal to 90 degrees:

$4\times90=360$

$360 º$

Look at the square below:

What is the size of angle A?

90°

Look at the square below:

What is the sum of the angles $D_1+B+A_1$?

$180$

Look at the square below:

What is the sum of the angles

$D_1+B$?

$135$

Look at the square below:

What is the size of angle $D_1$?

$45\degree$

Look at the square below:

What is the sum of the angles of the four triangles?

$720$