👤
a fost răspuns

1+3+...+39
1+3+...+75
20+40+...+220
Pls repede

Răspuns :

Nicoletastefan2004
1+3+...+39=2(1+2+...+20)+(-1)×39=2×20×21÷2-39=20×21-39=381
1+3+...+75=2(1+2+...+38)+(-1)×75=2×38×39÷2-75=1407
20+40+...+220=20(1+2+...+11)=20×11×12=220×12=2640.
Sper ca te am ajutat!:)

Alte intrebari