Question

Urgent.... Am nevoie, va rog! Dau coroană! Ex:9 Urgent

Answer 1

    ___
a)  aa , a ≠ 0 

11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99 = 495 
= ( 11 + 99) + ( 22 + 88) + ( 33 +77 ) + ( 44 + 66) + 55 =
= 110 + 110 + 110 + 110 + 55 
= 440 + 55 
= 495 

    ___
b) aaa,  a ≠0
111 + 222 + 333 + 444 + 555 + 666 + 777 + 888 + 999 = 4 995 
= (111 + 999 ) x 4 + 555 =
= 1 110 x 4 + 555 =
= 4 440 + 555 =
= 4 995 
   ____
c) aaaa,  a ≠ 0 

1 111 + 2 222 + 3 333 + 4 444 + 5 555 + 6 666 + 7 777 + 8 888 + 9 999 =
= ( 1 111 + 9 999 ) × 4 + 5 555 =
= 11 110 × 4 + 5 555 =
= 44 440 + 5 555 =
= 49 995