GRE Math : How to find an angle in a pentagon

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #1 : How To Find An Angle In A Pentagon

In a five-sided polygon, one angle measures . What are the possible measurements of the other angles?

Possible Answers:

Correct answer:

Explanation:

To find the sum of the interior angles of any polygon, use the formula , where n represents the number of sides of a polygon.

In this case:

The sum of the interior angles will be 540. Go through each answer choice and see which one adds up to 540 (including the original angle given in the problem).

The only one that does is 120, 115, 95, 105 and the original angle of 105.

Example Question #2 : How To Find An Angle In A Pentagon

In a particular heptagon (a seven-sided polygon) the sum of four equal interior angles, each equal to  degrees, is equivalent to the sum of the remaining three interior angles.

Quantity A: 

Quantity B: 

Possible Answers:

Quantity A is greater.

The two quantities are equal.

Quantity B is greater

The relationship cannot be determined.

Correct answer:

Quantity A is greater.

Explanation:

The sum of interior angles in a heptagon is  degrees. Note that to find the sum of interior angles of any polygon, it is given by the formula:

 degrees, where  is the number of sides of the polygon.

Three interior angles (call them )  are unknown, but we are told that the sum of them is equal to the sum of four other equivalent angles (which we'll designate ):

Further more, all of these angles must sum up to  degrees:

We may not be able to find , or , indvidually, but the problem does not call for that, and we need only use their relation to , as stated in the first equation with them. Utilizing this in the second, we find:

Example Question #3 : How To Find An Angle In A Pentagon

Pentagon2

What is the value of  in the figure above?

Possible Answers:

Correct answer:

Explanation:

Always begin working through problems like this by filling in all available information. We know that we can fill in two of the angles, giving us the following figure:

Pentagon2 2

Now, we know that for any polygon, the total number of degrees in the figure can be calculated by the equation:

, where  is the number of sides.

Thus, for our figure, we have:

Based on this, we know:

Simplifying, we get:

Solving for , we get:

 or 

Example Question #1 : How To Find An Angle In A Pentagon

Pentagon1

Quantity A: The measure of the largest angle in the figure above.

Quantity B: 

Which of the following is true?

Possible Answers:

The relationship cannot be determined.

Quantity B is larger.

Quantity A is larger.

The two quantities are equal.

Correct answer:

Quantity A is larger.

Explanation:

Pentagon1

To begin, recall that the total degrees in any figure can be calculated by:

, where  represents the total number of sides. Thus, we know for our figure that:

Now, based on our figure, we can make the equation:

Simplifying, we get:

 or 

This means that  is . Quantity A is larger.

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