Question

Calculați urmatoarele sume a) 2+4+6+8+...+200 b) 5+10+15+20+...+250

Answer 1

a) 2+4+6+..+200=

= 2(1+2+3+..+100)= 2$\frac{100x101}{2}$= 100x101=10100

b) 5+10+15+..+250=

=5(1+2+3+..+50)= 5$\frac{50x51}{2}$= 5x25x51=125x51=..