# Prove Triangle Inequality: $\frac{a}{\sqrt[3]{4b^3+4c^3}}+...<2$

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• anemone
In summary, the Triangle Inequality is a mathematical principle stating that in a triangle, the sum of any two sides must be greater than the third side. It is used in the given proof to show that the sum of the reciprocals of the cube roots of the sums of the cubes of the sides is less than 2. The notation in the statement represents the sides and sums of the triangle, and the Triangle Inequality can be proven using various methods. This concept is important in mathematics and has practical applications for solving problems involving triangles.
anemone
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MHB
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Let $a,\,b$ and $c$ be the side lengths of a triangle. Prove that $\dfrac{a}{\sqrt[3]{4b^3+4c^3}}+\dfrac{c}{\sqrt[3]{4a^3+4b^3}}+\dfrac{a}{\sqrt[3]{4b^3+4c^3}}<2$.

Since $\dfrac{b^3+c^3}{2}\ge \left(\dfrac{b+c}{2}\right)^2$, we have

$\sqrt[3]{4(b^3+c^3)}\ge b+c$.

From $b+c>a$, it follows that $2(b+c)>a+b+c$. Thus

$\dfrac{a}{\sqrt[3]{4(b^3+c^3)}}<\dfrac{a}{b+c}<\dfrac{2a}{a+b+c}$

Therefore

$\displaystyle \sum_{\text{cyclic}}\dfrac{a}{\sqrt[3]{4(b^3+c^3)}}<\sum_{\text{cyclic}}\dfrac{2a}{a+b+c}=2$

## 1. What is the Triangle Inequality?

The Triangle Inequality is a mathematical concept that states that the sum of any two sides of a triangle must be greater than the length of the third side.

## 2. Why is it important to prove the Triangle Inequality?

Proving the Triangle Inequality is important because it is a fundamental property of triangles and is used in many geometric and algebraic proofs. It also helps to ensure the validity of mathematical calculations and constructions involving triangles.

## 3. How do you prove the Triangle Inequality?

The Triangle Inequality can be proven using various methods, such as the Pythagorean Theorem, the Law of Cosines, and the Law of Sines. It can also be proven using algebraic manipulations and geometric constructions.

## 4. What is the purpose of the expression $\frac{a}{\sqrt[3]{4b^3+4c^3}}+...<2$ in the proof of the Triangle Inequality?

This expression is used to show that the sum of the two sides of the triangle is less than 2, which is the maximum possible value for the sum of two sides in order for the Triangle Inequality to hold true.

## 5. Can the Triangle Inequality be applied to any type of triangle?

Yes, the Triangle Inequality applies to all types of triangles, including equilateral, isosceles, and scalene triangles. It is a universal property of triangles and is not limited to any specific type.

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