1. Since in a parallelogram the angles located opposite each other are equal, the angle ВСD = angle BAD = 45 °.
2. Angle CBD = 45 ° according to the problem statement. In triangle BCD, both angles at the base BC are equal to 45 °.
Therefore, this triangle is isosceles and its sides BD and CD are equal.
3. СD = AB = 6 cm, since the opposite sides of the parallelogram are equal. Therefore, the side ВD, of the triangle ВСD, which is the diagonal of the parallelogram, is 6 cm.
Answer: the length of the diagonal of the parallelogram is 6 cm.
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