Răspuns:
Folosim formula sumei lui Gauss:
[tex]1 + 2 + 3 + ... + n = \frac{n(n + 1)}{2} [/tex]
f) 1/5 + 2/5 + 3/5 + 4/5 + ... + 9/5=
1+2+3+..+9/5= 9*10/2/5= 9*5/5= 9
g) 1/7 + 2/7 + 3/7 +4/7 + ... + 20/7=
1+2+3..+20/7= 20*21/2/7= 10*21/7= 10*3= 30
h)2/13 + 4/13 + 6/13 + ... + 50/13=
2(1+2+3+..+25)/13= 2*25*26/2/13= 25*26/13= 50
i) 3/8 + 6/8 + 9/8 + ... + 48/8=
3(1+2+3+...+16)/8= 3*16*17/2/8= 3*8*17/8= 3*17= 51
