limn→infty[1+2+3+⋯nn+2n2] is
12
1
-1
−12
limn→infty[1+2+3+⋯nn+2n2] =limn→∞[n(n+1)(n+2)n2]=limn→∞n2[n+1−n−2n+2] =limn→∞n2(−1n+2) =limn→∞−12(1+2n) =−12(1+0)=−12