SAT Math : How to find the area of a circle

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #41 : How To Find The Area Of A Circle

What is \(\displaystyle 320^{\circ}\) in radians?

Possible Answers:

\(\displaystyle \frac{16\pi}{9}\)

\(\displaystyle \frac{16}{9}\)

\(\displaystyle \frac{9\pi}{16}\)

\(\displaystyle \frac{\pi}{9}\)

\(\displaystyle -\frac{13\pi}{9}\)

Correct answer:

\(\displaystyle \frac{16\pi}{9}\)

Explanation:

To convert degrees to radians, we need to remember the following formula.

\(\displaystyle \mbox{degrees}\cdot \frac{\pi}{180}\).

Now lets substitute for degrees.

\(\displaystyle 320\cdot \frac{\pi}{180}=\frac{16\pi}{9}\)

Example Question #94 : Circles

A circle is circumscribed by a square, and that square is the base of a cube. If the volume of the cube is 216, what is the area of the circle?

Possible Answers:

\(\displaystyle 9\pi\)

\(\displaystyle 36\pi\)

\(\displaystyle 2\pi\sqrt{6}\)

\(\displaystyle 3\pi\)

\(\displaystyle 6\pi\)

Correct answer:

\(\displaystyle 9\pi\)

Explanation:

The equation for the volume of a cube is 

\(\displaystyle V=s^3\)

If V= 216, then s = 6. 

When a circle is circumscribed by a square the diameter of the circle is equal to the length of one side of the square. In this case, one side of the square is equal to 6; therefore the diameter of the circle is also 6. We can find the area of a circle with the equation 

\(\displaystyle A=\pi r^2\)

and since the radius is equal to half the diameter: 

\(\displaystyle A=\pi (3^2)=9\pi\)

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