Question

calcati urmatoarele sume:gauss:a)1+2+3+...+30,b)2+3+4+...+30,c)9+10+11+...+30

Answer 1

a)    

1+2+3…..30=(30+1)*30/2    

1+2+3…n=n(n+1)/2    

1+2+3…..30=(30+1)*30/2=31*15=465    

b)    

2+3+….30=(30+1)*30/2-1=464    

c)    

9+10+….30=(30+1)*30/2-(1+2….+8)=31*15-8*9/2=465-36=429