Question

k ( k - 1 ) = 5

ajudar aí ​

Answer 1

$\text{k(k-1)=5}$

$\text k^2 - \text k = 5$

$\text k^2 - \text k -5 = 0$

usando bhaskara

$\displaystyle \text k = \frac{-(-1)\pm\sqrt{(-1)^2-4.(-5)}}{2.1} \to \text k = \frac{1\pm\sqrt{1+20}}{2}$

$\displaystyle \text k = \frac{1\pm\sqrt{21}}{2}$

Soluções :

$\huge\boxed{\text k = \frac{1+\sqrt{21}}{2} \ \ ou\ \ \text k = \frac{1-\sqrt{21}}{2}}$