Answer:
[tex]T_n = \left \{ {{T_1=2} \atop {T_n =-5T_{n-1}}} n>1 \right.[/tex]
Step-by-step explanation:
Given
Geometric sequence: 2, -10, 50, -250
Required
Recursive formula of the sequence
We start by naming each sequence
[tex]T_1 = 2\\T_2 = -10\\T_3 = 50\\T_4 = -250[/tex]
Represent each term in relation to the previous term (except T1)
[tex]T_1 = 2\\T_2 =2 * -5\\T_3 = -10 * -5\\T_4 = 50 * -5[/tex]
Recall that
[tex]T_1 = 2\\T_2 = -10\\T_3 = 50\\T_4 = -250[/tex]
So, at this point; we have to make substitutions
[tex]T_1 = 2\\T_2 =T_1 * -5\\T_3 = T_2 * -5\\T_4 = T_3 * -5[/tex]
Subtract 1 from each term on the right hand side
[tex]T_1 = 2\\T_2 =T_{2-1} * -5\\T_3 = T_{3-1} * -5\\T_4 = T_{4-1} * -5[/tex]
Replace each term greater than 1 by n
[tex]T_1 = 2\\T_n =T_{n-1} * -5\\T_n = T_{n-1} * -5\\T_n = T_{n-1} * -5[/tex]
Remove repetition
[tex]T_1 = 2\\T_n =T_{n-1} * -5[/tex]
[tex]T_1 = 2\\T_n =-5T_{n-1}[/tex]
Hence, the recursive formula is
[tex]T_n = \left \{ {{T_1=2} \atop {T_n =-5T_{n-1}}} n>1 \right.[/tex]
