To explain why triangles ABD and CBD are congruent using the Side-Angle-Side (SAS) congruence theorem, it would be helpful to know the following information:
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The lengths of the relevant sides: You need to know that two sides of triangle ABD are equal in length to two sides of triangle CBD. Specifically, this would typically involve knowing the lengths of segments AB and CB.
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The length of the shared side: Triangle ABD and triangle CBD have a common side, which is AC in this context. To apply SAS, you would need to confirm this side is included between the two pairs of congruent sides.
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The included angle: You should also identify that the angle included between the two pairs of sides (angle ADB or angle CDB) is congruent. This included angle is necessary for applying the SAS theorem.
With this information, you could confidently use the SAS congruence theorem, which states that if two sides and the included angle of one triangle are equal to two sides and the included angle of another triangle, then the triangles are congruent.