Which of the following steps were applied to abcd to obtain a'b'c'd'?

It was reflected, when a figure is reflected, all points along each segment are reflected. In other words, a point lying on AB in the pre-image will lie on A'B' in the image. If point E is the midpoint of AB, then point E' will be the midpoint of A'B'. Therefore, a reflected figure preserves collinearity and betweenness of points, just like with translated figures. Also, if a line of symmetry exists in the pre-image, it will exist in the image.

according to the triangle sum theorem, all the angles in a triangle must add up to 180 degrees. if we know one angle is already 90, we do 180-90=90. the other 2 angles must add up to 90, exactly.

step-by-step explanation: