M is the midpoint of edge ad of parallelogram ABCD, and MB = MC. Can you explain that parallelogram ABCD must be a rectangle ten minutes

If MB = MC, then the triangle MCB must be isosceles triangle. Because the parallelogram complements the inner angle, the angle MBC = angle MCB = 45 degrees. So the angle ABC = angle DCB = 90 degrees. So the parallelogram ABCD is a rectangle

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