Question

Calculati sumele:
a) 3+6+9+12+...+60
b) 5+10+15+...+80
Va rog am nevoie urgent dau și coroană ​

Answer 1

Răspuns:

a)

3 + 6 + 9 + ... + 60 =

= 3 × ( 1 + 2 + 3 + ... + 20 )

= 3 × 20×21/2

= 3 × 10 × 21

= 10 × 63

= 630

b)

5 + 10 + 15 + ... + 80 =

= 5 × ( 1 + 2 + ... + 16)

= 5 × 16 × 17 / 2

= 5 × 8 × 17

= 680

Succes! ♡︎♥︎♡︎

Answer 2

a) 3•(1+2+3+4+…+20)
S=3• (20•21:2)
S=3•(10•21)
S=3•210
S=630

b)5•(1+2+3+…+16)
S=5•(16•17:2)
S=5•(8•17)
S=5•136
S=680