Q:
# What must one justify to prove that a quadrilateral ABCD is a parallelogram?

A:

Regents Prep explains that the quickest method for proving that a quadrilateral is a parallelogram is if one pair of opposite sides of the quadrilateral are both parallel and congruent. However, several other forms of proof exist as well.

According to Wikipedia, in Euclidean geometry, a parallelogram is a simple quadrilateral, with four edges and four corners, characterized by its two pairs of parallel sides. Because of its parallel orientation, the opposite sides of a parallelogram are equal in length. The opposite angles of a parallelogram are also equal in measure. This congruence is proven by Euclid's parallel postulate, also known as Euclid's fifth postulate; it is part of Euclid's "Elements," which serves as the basis for the shortest method of proof previously described.

The basic definition of a parallelogram lends itself to several other methods of proof. For instance, one can prove that a quadrilateral is a parallelogram if the two pairs of opposite angles in the quadrilateral are congruent. Further, if the consecutive angles in the quadrilateral are supplementary, or equal to 180 degrees, then it is a parallelogram. Finally, one can also prove a quadrilateral is a parallelogram if the two diagonals of the quadrilateral can bisect each other, or divide each other equally in half.

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Q:
## How did southerners justify secession?

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Full Answer >**When South Carolina seceded from the Union in 1860, the main justification of secession was that southerners believed secession was the only way they could preserve their institution of slavery.**Not all southerners supported secession, however, but those who did argued that because the southern states were a part of the Union, their rights should be respected by the federal government.Filed Under: -
Q:
## What is the "ABCD" test of moles for melanoma?

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Full Answer >**The ABCD test is a tool used to remember the signs of melanoma, reports the American Melanoma Foundation.**The letters stand for asymmetry, border irregularity, color and diameter.Filed Under: -
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## What is the side splitter theorem?

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Full Answer >**The side splitter theorem states that if a line parallel to one side of a triangle intersects with the other two sides, it divides those two sides proportionally.**This theorem can be used to solve many similar triangle math problems.Filed Under: -
Q:
## How many degrees are in a right angle?

A:A right angle has 90 degrees. Angles are measured on a scale from 0 to 360 degrees. Right angles represent one-fourth of a full 360-degree revolution.

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