Question

5+10+15+.....75
36+42+48+....150

Answer 1

Răspuns:

Explicație pas cu pas:

5 + 10 + 15 + ..... + 75 = 600

= 5 × ( 1 + 2 + 3 + ..... + 15 ) =

= 5 × 15 × ( 1 + 15 ) : 2 =

= 75 × 16 : 2 =

= 75 × 8 =

= 600

__________________________

36 + 42 + 48 + ...... + 150 = 1860

= 6 × ( 6 + 7 + 8 + ...... + 25 ) =

               (25 - 6 + 1 = 20 termeni are suma )

= 6 × 20 × ( 6 + 25 ) : 2 =

= 60 × 31 =

= 1860