A rectangle is a parallelogram which internal angles are all 90°
To find if the given parallelogram is a rectangle, we should:
• Find the slope of the segment AB
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• Find the slope of the segment BC
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• Multiply both results. If the product is -1, then AB and BC are perpendicular
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• Find the slope of DC
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• Find the slope of AD
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• If the slope of DC is equal to the slope of AB, both segments are parallel
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• If the slope of AD is equal to the slope of BC are equal, both segments are parallel
If all the conditions above are met, the parallelogram is a rectangle