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16 Gâsiti si scoateti un factor comun, apoi calculati urmãtoarele sume:
a 5+10+15+20+..+1000;
b8+16+24+32+...+4000;
c 11 + 22 + 33 + 44 + ... + 7700;
d 21 + 42 + 63 + 84 + ... + 2100;
e4 + 8 + 12 +16+..+400;
{25 + 50 + 75 + 100 + ... + 400;
g10 + 20 + 30 + 40 + ... + 480;
h6 + 12+18+24+..+1200;
130 +60 + 90 + 120+...+ 900;
115 + 30 + 45 + 60 + ... + 600.
Rezolvare: a 5 + 10 + 15 + 20+... + 1000 = 5•1+5•2+5.3+5.4+...+5.200 =
=5. (1+2+3+4+...+200) =5•200 • (200 + 1) :2=5•200 • 201:2 =
= 5.100 • 201 = 100 500.

VA ROOOG REPEDEEEE DOAR LA (c,d,e,f)