Adjusting the angles at all the vertices to get the new shape without changing the number of sides is possible. If one angle is increased, another angle must be decreased by the same value, otherwise the polygon will no longer be closed. The sum of the angles does not change using this operation. In general, with regular polygons all sides and angles are equal , each angle is equal to:.

### Geometry Worksheets for Practice and Study

Adjust the slider to change the number of sides n on the polygon below. Click "View Triangles" to see each angle of the polygon, as well as the sum of its interior angles. Number of Sides:. More MathApps. Download Help Document. Figure An altitude drawn to the hypotenuse of a right triangle. Theorem The altitude drawn to the hypotenuse of a right triangle creates two similar right triangles, each similar to the original right triangle and similar to each other.

Figure shows the three right triangles created in Figure They have been drawn in such a way that corresponding parts are easily recognized. Because the triangles are similar to one another, ratios of all pairs of corresponding sides are equal. This produces three proportions involving geometric means. Theorem If an altitude is drawn to the hypotenuse of a right triangle, then each leg is the geometric mean between the hypotenuse and its touching segment on the hypotenuse. Theorem If an altitude is drawn to the hypotenuse of a right triangle, then it is the geometric mean between the segments on the hypotenuse.

Example 3: Use Figure to write three proportions involving geometric means. Figure Using geometric means to write three proportions. Figure Using geometric means to find unknown parts. Figure An altitude drawn to the hypotenuse of a right triangle to aid in deriving the Pythagorean Theorem. See Figure for the parts of a right triangle.

Figure Parts of a right triangle. Figure Using the Pythagorean Theorem to find the hypotenuse of a right triangle.

## Geometry Interactive Notebook Activities and Scaffolded Notes Bundle

Therefore, is called a Pythagorean triple. Some other values for a, b, and c that will work are and Any multiple of one of these triples will also work. For example, using the , , and are also Pythagorean triples. Example 7: Use Figure to find x. Figure Using the Pythagorean Theorem to find a leg of a right triangle. You can also find x by using the Pythagorean Theorem. Figure Using the Pythagorean Theorem to find the unknown parts of a right triangle.

The converse reverse of the Pythagorean Theorem is also true. Extension to the Pythagorean Theorem Variations of Theorem 66 can be used to classify a triangle as right, obtuse, or acute. In each case, c represents the longest side in the triangle. If the values can be the sides of a triangle, then classify the triangle. Because its sides are of different lengths, it is also a scalene triangle. Because two of its sides are of equal measure, it is also an isosceles triangle.

Because all sides are of different lengths, it is also a scalene triangle. Special Right Triangles Isosceles right triangle. An isosceles right triangle has the characteristic of both the isosceles and the right triangles. It has two equal sides, two equal angles, and one right angle. Figure An isosceles right triangle. Figure The ratios of the sides of an isosceles right triangle. Method 2.

Example If the diagonal of a square is 6 2, find the length of each of its sides. Method 1: The diagonal of a square divides it into two congruent isosceles right triangles. Figure A diagonal of a square helps create two congruent isosceles right triangles. Method 2: Use the Pythagorean Theorem. Example What are the measurements of x, y, and z in Figure ? Figure Finding the unknown parts of this right triangle.

Consequently, the other two sides must be 4 3 and 2 4 , or 8. The hypotenuse is 2x.

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The hypotenuse is Figure is an equilateral triangle. Figure Using the perimeter of an equilateral triangle to find an altitude. Determine whether the following sets of three numbers can be the lengths of sides of a triangle. If they can be, then classify the triangle. Chapter 7: Right Triangles 3.

If the hypotenuse of a right triangle is exactly twice as long as the shorter leg, what is the degree measure of the smallest angle in the triangle? Compute the base of an isosceles right triangle with legs 3 in long. Here you will learn about some important angles that are determined using circles, and you will explore some connections between properties of circles and properties of regular polygons.

Before these efforts are undertaken, you want to make sure that you are familiar with some conventions involving the terminology and notation.

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Parts of Circles A circle is a special figure, and as such has parts with special names. There are also special angles, lines, and line segments that are exclusive to circles. In this chapter, we shall examine all of them. Circles are named by naming the center.

### Geometry Rules: Angles and Lines

The plural of radius is radii. R Y T M Q X From the definition of radius and diameter, it is clear that all radii of a circle are equal in length and all diameters of a circle are equal in length. In Figure circle Q AB is a secant. CE is a tangent. In Figure Lines l and m are common tangents. Figure Internal and external common tangents to circles. Perhaps the one that most immediately comes to mind is the central angle. Central angles Central angles are angles formed by any two radii in a circle.

## Classifying Polygons

The vertex is the center of the circle. Figure A central angle of a circle. It consists of two endpoints and all the points on the circle between these endpoints. The symbol! This symbol is written over the endpoints that form the arc.

It is named using three points. The first and third points are the endpoints of the diameter, and the middle point is any point of the arc between the endpoints. A minor arc is named by using only the two endpoints of the arc. It is named by three points. The first and third are the endpoints, and the middle point is any point on the arc between the endpoints. In Figure , AC is a diameter. ABC is a semicircle. Figure A diameter of a circle and a semicircle. Figure A minor arc of a circle. Figure A major arc of a circle.

T S Q U Arcs are measured in three different ways. Its unit length is half of the circumference of the circle. Its unit length is a portion of the circumference. Its length is always less than half of the circumference. Its unit length is a portion of the circumference and is always more than half of the circumference. Figure Degree measure and arc length of a semicircle. Figure Finding degree measures of arcs. Theorem In a circle, if two central angles have equal measures, then their corresponding minor arcs have equal measures.

Theorem In a circle, if two minor arcs have equal measures, then their corresponding central angles have equal measures. Then the measure of a minor arc equals the measure of its corresponding central angle.