SAT Study Guide/Part 2 - The Math Section/Concepts from Geometry
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The SAT generally does not test any arcane or difficult geometry; however, it is important to know several rules.
Degrees and Angles 
- A circle contains 360 degrees. Every circle contains 360 degrees. Each degree is 1/360 of the total distance around the outside of the circle.
- A line is a 180-degree angle. A line is a flat angle. Half a circle, or a semicircle, is also a 180 degree angle.
- When two lines intersect, four angles are formed.
- If two lines are perpendicular, their slopes are negative reciprocals. If line A has a slope of 3, and line B is perpendicular to A, it has a slope of -1/3.
- When two lines intersect, the angles opposite each other will have the same measures. These are known as vertical angles. The total of all four angles created is 360 degrees.
- The sum of the lengths of any two sides of a triangle must be larger than the length of the remaining side.
- A rectangle + two triangles on opposite sides = a trapezoid.