S.1 數學 THX... (sequence) 急！！！！！！

a) 1, 4, 7, 10, 13 ...
general term : 3n-2,,,the 10th term: 3(10)-2 = 28

b) 32, 25, 18, 11 ...
general term : -7n +39,,,the 10th term: -7(10) +39 = -31

c) 3, 9, 27, 243 ...
general term : 3^n,,,the 10th term: 3^10

a) general term : T(n):1+3(n-1)
10th term:28
b) general term : T(n):32-7(n-1)
10th term:-31
c) general term : T(n):3*3^(n-1)
10th term:59049

a) 1, 4, 7, 10, 13 ...

T(5)-T(4)=T(4)-T(3)=T(3)-T(2)=T(2)-T(1)=3
d=3
a=1
T(n)=a+(n-1)d
T(10)=1+(10-1)3
=28

b) 32, 25, 18, 11 ...

T(4)-T(3)=T(3)-T(2)=T(2)-T(1)=-7
d=-7
a=32
T(n)=a+(n-1)d
T(10)=32+(-7-1)7
=-24

c) 3, 9, 27, 243 ...

T(4)/T(3)=T(3)/T(2)=T(2)/T(1)=3
T(n)=ar^n-1
T(10)=3(3)^10-1
=59049

a) the first term = 1
common difference = 4-1 = 3
General term = 1+(n-1)*3 = 3n-2
T(10) = 3(10) - 2 = 28

b) first term = 32
common difference = 25-32 = -7
general term = 32 + (n-1)*(-7) = 39-7n
T(10)= 39 - 7(10) = -31