Question

求解1十［（n—1）［6十6（n一1）］/2过程.它答案是3n^2一3n十1,

Answer 1

1十［（n—1）［6十6（n一1）］/ 2

=1+［6（n—1）十6（n一1）^2］/ 2

=1+［6n—6）十6（n^2一2n+1）］/ 2

=1 +( 6n -- 6+ 6n ^2 - 12n + 6 ) / 2

=1+ (6 n^2 – 6n ) /2

=1 + 3^2 – 3n

= 3^2 – 3n+1