Use the definition of congruence in terms of rigid motions to show that two triangles are congruent if and only if corresponding pairs of sides and corresponding pairs of angles are congruent.
Sample Practice Questions (3)
1
Triangle ABC has vertices A(1,2), B(4,2), and C(1,6). Triangle A′B′C′ has vertices A′(−1,2), B′(−4,2), and C′(−1,6). Which rigid motion maps △ABC onto △A′B′C′, proving they are congruent?
AA reflection over the y-axis.
BA reflection over the x-axis.
CA translation 2 units to the left.
DA rotation of 90∘ counterclockwise about the origin.
In the coordinate plane shown below, △ABC has vertices A(1,1), B(4,1), and C(1,3). △A′B′C′ has vertices A′(−1,1), B′(−4,1), and C′(−1,3). Which rigid motion maps △ABC onto △A′B′C′?
Triangle RST is shown on the coordinate plane with vertices R(2,2), S(5,2), and T(2,4). If △RST is translated by the rule (x,y)→(x−6,y−2) and then reflected over the x-axis to form △R′′S′′T′′, what are the coordinates of S′′?