Question

s= (-5)+(-4)+(-3)+.....+(+18)+(+19)+(+20)=
va roggg​

Answer 1

Răspuns:

Explicație pas cu pas:

s=-(5+4+3+2+1)+(1+2+....+20)=-(5×6/2)+(20×21/2)=-15+210=195

suma Gauss=1+2+3+...+n=n(n+1)/2

Answer 2

$S = (-5)+(-4)+(-3)+..+(+18)+(+19)+(+20) \\ S = (+20)+(+19)+(+18)+...+(-3)+(-4)+(-5)\\ \\ 2S = 15+15+15+\underset{de~26~ori}{\underbrace{...}}+15+15+15\\ \\ 2S = 15\cdot 26 \\\\ S = \dfrac{26\cdot 15}{2} \\ \\S = 13\cdot 15\\ \\ \boxed{S = 195}$