### For sure you have read about special right triangles, and how it is stated that the side opposite to the 30° angle helps to define the other two sides in a 30°-60°-90°, and the legs in a 45°-45°-90° are used to define the hypotenuse; but you still don't know why this is true!

### You will learn in this lesson why, and how you may remember it in the future. We start with an equilateral triangle to find the 30°-60°-90° side relationship, and we continue with a square to find the 45°-45°-90° side relationship; this way you will interiorize in your mind the concepts and they will come to you whenever you need them again in a problem solving process! When a similar version is given to solve, to work it on the screen you will use your stylus and the marker tools menu.

** Lesson's Content **

** Lesson's Glossary **

**Acute triangle **

A triangle whose angles are acute.

**Altitude **

Height

**Altitude of a triangle **

The perpendicular segment from a vertex to the line containing the opposite side of a triangle.

**Angle bisector **

A ray that is in the interior of an angle and forms two equal angles with the sides of that angle.

**CPCTC**

**Corresponding Parts of Congruent Triangles are Congruent.**

**Equilateral triangle **

A triangle whose sides are equal in length.

**Isosceles triangle **

A triangle with two sides of equal length.

**Median **

The segment connecting the vertex of an angle in a triangle to the midpoint of the side opposite it.

**Obtuse triangle **

A triangle with one acute angle.

**Perpendicular bisector **

The bisector of a segment perpendicular to it.

**Right triangle **

A triangle that has a 90 degree angle.

**Scalene triangle **

A triangle with no equilateral sides.

**Triangle **

A polygon with three sides.

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