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**Lines that intersect **

When lines intersect, there are certain facts that arise that help us to do calculations:

- Two lines crossing each other as in our illustration will produce an “
**X**” shape and the following will always hold: - The angles that are “opposite” to each other, or more precisely “
**vertically opposite**” are equal in size. So the red angles are equal and the green angles are equal. - If we added the value of all the angles in this figure they always add to
**360ᵒ**

A straight line is said to have an angle of **180ᵒ** at any point along it, so if we create two or more angles at a specific point, the total of the angles at that point will always add to **180ᵒ. **