Question

calculați potrivit sumă tuturor numerelor naturale consecutive
a)mai mici sau egale cu 20
b)mai mici sau egale cu 31

Answer 1

a)
1+2+3+....+20= 20*21/2=10*21=210

b)
1+2+3+...31=31*32/2=31*16=496

/=supra (in caz ca nu stiai )

Answer 2

a 
1+2+3+4+5+6+7+8+9+10+12+13+14+15+16+17+18+19+20=
1+2+3+....+20=
20+19+...+1=
s2=21x20
s2=420:2=210

b  
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31
1+2+...+31
31+29+...+1=
s2=32x31
s2=992:2
s=496