Question

sum of the e series S = 1+1/2(1+2)+1/3(1+2+3)+1/4(1+2+3+4).......what is the 20th term?????? ​

Answer 1

Answer:

20(1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)+1

Answer 2

Answer:

Step-by-step explanation:

en  S=1+12(1+2)+13(1+2+3)+……..120(1+2+3+……20)  

=∑20n=11n∑n  

=∑20n=11nn(n+1)2  

=∑20n=112(n+1)  

=12∑20n=1(n+1)  

=12[n(n+1)2+n]200  

=12[20(21)2+20]  

=5(21)+10  

=115