Final answer:
The correct rigid transformations to map congruent triangle ABC onto triangle DEC are a reflection followed by a rotation or a reflection followed by a translation; dilation is not required as congruent triangles are the same size.
Step-by-step explanation:
Given that triangles ABC and DEC are congruent by the Side-Side-Side (SSS) congruence theorem, there are several rigid transformations that can be used to map triangle ABC onto DEC. A rigid transformation is a transformation of a geometric figure that preserves distances and angles. The options include combining reflection, rotation, translation, or dilation. However, considering the congruence, the correct sequence would be a reflection followed by a rotation or a reflection followed by a translation. Dilation would not be needed since congruent triangles are equal in size, and a dilation would change the size of the triangle.
Rotation is defined by the transformation equations x' = x cos Ø + y sin Ø for the x-coordinate, and y' = -x sin Ø + y cos Ø for the y-coordinate. This transformation maintains the distances between points, therefore keeping congruence intact.