How to prove a quadrilateral is a parallelogram with slope and distance?

If it is on a coordinate plane:
1. Mark opposite lines and find their slopes.
2. If you see that they are the same, that means that they are parallel. 
3. Now, you have to check if the opposite lines measure the same distance. If the distance is already given, then make sure it is the same. If it isn't, you can use the distance formula and verify if the opposite lengths are the same.

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the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.

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