15)
[tex]\it x\in\Big(0,\ \dfrac{\pi}{2}\Big),\ sinx=\dfrac{2}{7}\\ \\ cosx=\sqrt{1-sin^2x}=\sqrt{1-\dfrac{4}{49}}=\sqrt{\dfrac{45}{59}}=\sqrt{\dfrac{9\cdot5}{49}}=\dfrac{3\sqrt5}{7}\\ \\ \\ tgx=\dfrac{sinx}{cosx}=\dfrac{\dfrac{2}{7}}{\dfrac{3\sqrt5}{7}}=\dfrac{2}{3\sqrt5}=\dfrac{2\sqrt5}{15}\\ \\ \\ ctgx=\dfrac{1}{tgx}=\dfrac{15}{2\sqrt5}=\dfrac{15\sqrt5}{2\cdot5}=\dfrac{3\sqrt5}{2}[/tex]
