GMAT students: are you struggling with geometry concepts? Are you frustrated by triangle and circle ratios? Did you boycott Pi Day yesterday (3/14) and eat cake instead? You are not alone!

As the narrator of this video notes, one of the trickier relationships in geometry – and one that has led to many a GMAT geometry mistake – is the concept that pi relates directly to the radius and not the diameter, leaving the potential for easy-to-overlook error when assigning a value to the radius/diameter for proportional difference purposes, or quickly plugging in a given diameter into the area formula (A = pi * r^2). It’s quite easy and pretty natural to say “let’s call the diameter 1”, but that means that you’re dealing with a radius of 1/2, and the radius is what goes into the area formula!

Watch the video and see what we mean:

While the GMAT is unlikely to adopt the video’s proposal for the constant Tau, noting the tricky relationship between diameter, radius, area, and circumference can help you to avoid that easy-to-commit family of mistakes on test day.

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## A Pi in the Sky Proposal

*Posted on March 15, 2011, filed in: GMAT*

Where is the video?

Hey Rakesh,

It should be back now…it’s disappeared once or twice today, though, so here’s the link as well: http://www.youtube.com/watch?v=jG7vhMMXagQ&feature=player_embedded