GMAT Geometry Strategy

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Geometry is fairly unique among GMAT Quant topics. There are many more rules you must memorize (area, perimeter, triangle ratios, etc.), and there's often a diagram accompanying the question. That doesn't mean you can treat geometry as completely separate from the rest of GMAT math, but there are a few issues to focus on.

1. Memorize the Rules

You can't get around it. You have to know the 30:60:90 triangle ratio. You'll be tested on the area of a circle. There are plenty of GMAT questions that you can't fake your way through--if you don't know that basic content, you'll miss them. They can be cheap points, but only if you do the work.

2. Apply the Rules

This sounds obvious, but bear with me. It takes some time to learn all the rules, but once you know them, there isn't much that the GMAT can keep hidden. If there are triangles in a question, there are only so many rules that could possibly apply.

If you're stuck on a geometry question, use the process of elimination. Think through all of the techniques you know that could possibly be relevant. One of them is probably what you need to use to solve the problem.

3. Look For Connections

Many GMAT geometry questions involve multiple figures. Sometimes there's a circle inscribed in a triangle; other times there are several adjacent triangles.

If there is more than one recognizable shape in a diagram, there is a connection. Look for what one of the figures tells you about the other. Perhaps the diagonal of a square is the same as the radius of a circle. Or the height of one triangle is the hypotenuse of another. Whatever the connection, it is probably the key to answering the question.

4. Re-draw Diagrams

If there is any complexity to a diagram at all, replicate it on your scratch paper. You'll instantly get a better understanding of the figure, and you'll be able to jot down notes, such as the measure of a certain angle.

5. Mark Up Diagrams

Once you've drawn a diagram on your scratch paper, figure out all the details you possibly can. If two of the angles in a triangle are given as 70 and x, you can determine that the third angle is 180 - 70 - x, or 110 - x. Note that on the diagram! Steps like that, even though they may seem obvious at first glance, are often the difference between solving a problem and staying stuck on it.

6. Keep an Open Mind

While most geometry problems stay within the bounds of geometry, some don't. A great example is Problem Solving #229 in the 12th edition of the Official Guide. It sounds like a geometry question ("Right triangle PQR is to be constructed in the xy-plane...") but it ends up testing combinatorics ("How many different triangles with these properties could be constructed?")

The tougher the problem, the more likely it crosses boundaries. Don't fall into the trap of seeing a problem, deciding that it's a certain type of question, and limiting yourself to the techniques you know for that specific type. Looking for connections shouldn't be limited to the links between figures in a diagram; it applies just as well to links between topics on GMAT math.



About the author: Jeff Sackmann has written many GMAT preparation books, including the popular Total GMAT Math, Total GMAT Verbal, and GMAT 111. He has also created explanations for problems in The Official Guide, as well as 1,800 practice GMAT math questions.

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