Question

sa se Calculeze suma nr nat luate din 7 in 7 pornind de la 200 la 1964 ! am nevoie pt teza!

Answer 1

200 / 7 = 28 rest 4 ⇒  200 = 7*28+4
1964/7 = 280rest 4 ⇒ 1964 = 7*280+4
1964 = 200 + 1764 = 200 + 7*452  intrucat  1764 / 7 = 452
Fie,
S=200+207+214+221+..+1964=200+(200+7*1)+(200+7*2)+ (200+7*3)+(200+7*452)=
 = 200+200+200+......+200 + 7*(1+2+3+.......452) =
 = 200*453 + 7 * (452*453) / 2 = 90600 + 7 * 204756 / 2 =
= 90600 + 7*102378 = 90600 + 716646 = 807246