a)1/1*2+2/ 2*3+.....+1/n(n+1)=n/n+1 b)1/1*3+1/3*5+...+1/ (2n-1) (2n+1)=n/2n +1 c)1/1*4+1/4*7+...+1/(3n-2)(3n+1)=n/3n+1


dau coraoana cu explicatii pls​