Find the `20^( th) ` term of the series `2 xx 4+4 xx 6+6 xx 8+. . .,+` n terms.

Explanation

`a_n=n^ th ` term of `(2,4,6, . .) xx n^ th ` term of `(4,6,8, .)=[2+(n-1) 2] xx[4+(n-1) 2]=2 n xx(2 n+2)`

`a_20=4 xx 20^2+4 xx 20=1600+80=1680``,`