maths求數形

1) n/2 [ 2(98) + (n-1)7 ]
=n/2 [ 2(98) + 7n - 7 ]
=98n + (7n^2)/2 - (7n)/2
=(7n^2)/2 + 28n

2) n/2 [ 2(2) + (n-1)11 ]
=n/2 [ 2(2) + 11n - 11 ]
=2n + (11n^2)/2 - (11n)/2
=(11n^2)/2 + (7n)/2

3) (1/3) (1/3)^(n-1)
=1/3^n