Question

1+2+3+........+90=
Calculati

Answer 1

SE APLICA REGULA LUI Gauss    1+2+3+,,,,,n=n·(n+1)/2          
1+2+,,,,,,,,,,90=90·91/2=45·91=4095

Answer 2

$\displaystyle 1+2+3+...+90= \frac{90(90+1)}{2} = \frac{90 \times 91}{2} = \frac{8190}{2} =4095$