If a triangle has side lengths 5 cm, 18
cm, and 12 cm, is it a right triangle?

No, it's not a right triangle.

Step-by-step explanation:

1. The Pythagorean Theorem states that the area of the square whose side is the hypotenuse (longest side of a right triangle) is equal to the sum of the area of the squares from the two other sides.

2. The longest side in this "triangle" has 18 centimeters, and the other 2 sides are 5 and 12 centimeters.

3. Let's apply the Pythagorean Theorem to see if 5^2 + 12^2 = 18^2

4. Okay, so the sum of the area of the squares from the two other sides is not equal to the hypotenuse squared, therefore, it's not a right triangle.

(Plus, it's not even a triangle because 7 < x < 17, and the third "side", 18, is not between 7 and 17.)

step-by-step explanation:

you can add the two numbers and divide the result by 2. or you can find the gap between the two numbers and add half of this to the smaller number.