Question

1+2+3+4+5+........+13=x la puterea a 2 cât este x

Answer 1

$1+2+3+...+13= \frac{n(n+1)}{2} = \frac{13(13+1)}{2}$

$\frac{13(13+1)}{2} = x^{2}$

$\frac{13*14}{2} = x^{2}$

$13*7= x^{2}$

$x^{2} =91$

$x= \sqrt{91} =9,54$