Pythagorean Theorem and 45°-45°-90° Triangles

Ever wondered how to find the missing side of a right triangle? The Pythagorean theorem is your answer! It states that in any right triangle, the square of the hypotenuse (longest side) equals the sum of the squares of the two legs (shorter sides): a² + b² = c².

The hypotenuse is always opposite to the right angle, while the legs form the right angle. This simple formula helps you solve countless geometry problems by finding unknown side lengths.

A special type of right triangle is the 45°-45°-90° triangle. These triangles have equal legs and follow a specific proportion. If both legs have length a, the hypotenuse will always equal a√2. You can prove this with the Pythagorean theorem:

1. a² + a² = c²
2. 2a² = c²
3. c = a√2

Helpful Tip: When you see a 45°-45°-90° triangle, you can immediately know that if the legs are 5 units long, the hypotenuse will be 5√2 units—no need to calculate!

Special Triangles and the Triangle Inequality Theorem

The 30°-60°-90° triangle is another special right triangle formed by cutting an equilateral triangle in half. In this triangle, if the shortest side is length a, the hypotenuse will be 2a, and the remaining side will be a√3. You can verify this using the Pythagorean theorem.

An important principle to remember is that the largest side of any triangle is always opposite to its largest angle. Similarly, the smallest side is opposite to the smallest angle. This relationship helps you visualize triangles better.

The Triangle Inequality Theorem (or Third Side Rule) states that the sum of any two sides must be greater than the third side. For example, in a triangle with sides 3 and 5, the third side must be less than 8 but greater than 2, so: 2 < c < 8. This theorem helps determine if a triangle can exist with given side lengths.

Remember: For any triangle to exist, all three inequalities must be true: a+b>c, a+c>b, and b+c>a. Similarly, the difference between any two sides must be less than the third side.