Get Posts Via Email

SAT and College Admissions Blog

Tricks and Traps: Squares Inscribed in Circles

Posted by Vicki Wood on Oct 5, 2011 8:26:00 AM

geometryIf you see a square inscribed in a circle on the SAT, the test makers are assessing your knowledge of 45:45:90 triangles.

What? Huh? The question is about squares and circles, not triangles! Listen closely, my SAT cohorts: Hidden triangles are often the key to solving the most difficult geometry questions.

Let’s look at an example of an inscribed square problem:


Begin by labeling the diagram with the information provided in the question. Notice that the diameter of the circle is also the diagonal of the square:


If you can find the length of the diagonal, you can find the diameter and radius. Use your knowledge of triangles to find this information:


The two triangles are 45:45:90 triangles, so the hypotenuse is the length of the side multiplied by the square root of 2. The radius is one-half of the diameter:


Now that you know the radius of the circle, you can solve for the area:


The correct answer is (C).

Always be on the lookout for hidden triangles on SAT geometry questions. If you graced with a questions that has a square inscribed in a circle, know that the diagonal of the square, found using 45:45:90 triangle properties, leads to the discovery of the radius.

PowerScore Practice Prep

Can you solve the following math questions? The solutions are listed below.

  1. A square is inscribed in a circle. The area of the circle is 50π. What is the perimeter of the square?
  2. A square is inscribed in a circle. If the area of the square is 36, what is the circumference of the circle?
  3. A square is inscribed in a circle. If the diameter of the circle is 4, what is the area of the square?

What are some of your favorite SAT Math tricks and techniques? Tell us in the comments!

Topics: SAT Prep

Subscribe to Email Updates

Free Trial! Try the first lesson of our Live online SAT Course for Free!