Geometry Formulas


The SAT makers love to play tricks and lure you in with some wrong answers so you need to know everything to handle those tricks. Usually, the geometry formulas you are given are very basic i.e. the area of a circle, of a rectangle, and of a triangle. You might be given areas of cylinder and a box that are less known and not very basic. So, you just need to multiply the 2-D area of one side by the extra dimension.

Then we have Pythagorean theorem. Again, this should be on your fingertips. Though the last two are not memorized often enough and they come up constantly on the SAT. Keep in mind that there are two special right triangles, 30°-60°-90° and 45°-45°-90° and you might be requiring their proportions. Also, go back and review the reference information at the beginning of the section whenever you see a 30, 60, or 45 in a triangle. If you are confident with the info, then keep an eye out for those angle measurements.

Important Geometry Formulas

  1. Parallel lines crossed by a transversal have many equal angles:
    Geometry Formulas 1
    In the above figure, m and n are parallel. If you see that information on your SAT, you will to be able to fill in a whole lot of other information quite quickly.
  2. A line drawn from a tangent’s point of intersection to the circle’s center makes a right angle with the tangent:
    Geometry Formulas 2
    This usually come in handy while dealing with some complicated figures that require you to fill in a lot of measurements based on a very little information provided to you.
  3. A regular hexagon can be broken into six equilateral triangles:
    Geometry Formulas 3
    Though this doesn’t come up very often. You might see it on your test once but it’s worth knowing to get an edge over others. Keep in mind that it’s not just the angles that are equal, every shorter line segment is also equal.


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