6. a) \(\frac{x^2}{y^2} + \frac{y^2}{z^2} + \frac{z^2}{x^2} \geq 3\) b) \(\frac{y}{x} + \frac{x}{z} + \frac{z}{y} \geq 3\) \(\frac{1}{a+b+c} + \frac{1}{b+c-a} + \frac{1}{c+a-b} \geq \frac{1}{a} + \frac{1}{b} + \frac{1}{c}\)