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Defining Congruence in Terms of Rigid Motions. Adapted from Walch Education. Key Concepts. If the figure has undergone only rigid motions (translations, reflections, or rotations), then the figures are congruent.
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Defining Congruence in Terms of Rigid Motions Adapted from Walch Education
Key Concepts • If the figure has undergone only rigid motions (translations, reflections, or rotations), then the figures are congruent. • If the figure has undergone any non-rigid motions (dilations, stretches, or compressions), then the figures are not congruent. A dilation uses a center point and a scale factor to either enlarge or reduce the figure. A dilation in which the figure becomes smaller can also be called a compression. 1.4.2: Defining Congruence in Terms of Rigid Motions
Key Concepts, continued • A scale factor is a multiple of the lengths of the sides from one figure to the dilated figure. The scale factor remains constant in a dilation. • If the scale factor is larger than 1, then the figure is enlarged. • If the scale factor is between 0 and 1, then the figure is reduced. 1.4.2: Defining Congruence in Terms of Rigid Motions
Key Concepts, continued • To calculate the scale factor, divide the length of the sides of the image by the lengths of the sides of the preimage. • A vertical stretch or compression preserves the horizontal distance of a figure, but changes the vertical distance. • A horizontal stretch or compression preserves the vertical distance of a figure, but changes the horizontal distance. 1.4.2: Defining Congruence in Terms of Rigid Motions
Key Concepts, continued • To verify if a figure has undergone a non-rigid motion, compare the lengths of the sides of the figure. If the sides remain congruent, only rigid motions have been performed. • If the side lengths of a figure have changed, non-rigid motions have occurred. 1.4.2: Defining Congruence in Terms of Rigid Motions
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