Question

calculați (2+4+6+8+.....+20)-(1+3+5+...+19) va rooooog​

Answer 1

Explicație pas cu pas:

S1=2+4+6+8+....+20=>

S1=2(1+2+3+4+...+10)=>S1=2*10*11/2=>S1=10*11

S2=1+3+5+....+19

S2=19+17+15+...+1 =>

2*S2=20+20+....+20

Ne trebuie acum cati de 20 avem dica nr de termeni a lui S2

n=(19-1)/2+1=>n=9+1=>n=10

=>2*S2=10*20=>S2=10*10

S1-S2=10*11-10*10=10(11-10)=10*1=10