Question

Ajutați mă va rog cam urgent la ex 1 punctul C si ex 2 si 3

Answer 1

1.c)
10+20+30+...+120=
=10·(1+2+3+...+12)=
=10·(12·13)/2=780   -> Linia 2. A)

2)
3·x+8·y+10·z=
= 3·x+3·y+5·y+10·z=
=3(x+y)+5(y+2·z)=
=3·10+5·12=
=30+60=90

3)
x+2·x+3·x+...+10·x=385
x·(1+2+3+...+10)=385
x·(10·11/2)=385
x·55=385
x=385:55
x=7