Question

S=(10+20+30+............+220) - (2+4+6+...........+30)

Answer 1

S=(10+20+30+............+220) - (2+4+6+...........+30)
S=S1- S2

S=(10+20+30+............+220)=10(1+2+3+.....+22)
in paranteza se recunoaste o suma Gauss cu formula de calcul:S=[n(n+1)]:2
=10×{[22×(22+1)]:2}=
2530
S2=2(1+2+3+........+15)=2×{[15×(15+1)]:2}==2×15×16:2=240

S=S1-S2=2530-240=2290