5. Recursion and Iteration
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-2, -8, -36, -174, -862
a_1&=-2 a_(n+1)&=5a_n+2n To do so, we will use a table. To find a_2, we will substitute 1 for n in the above formula. To find a_3, we will substitute 2 for n, and so on.
| n | a_(n+1)=5a_n+n | 5a_n+n | a_(n+1) |
|---|---|---|---|
| - | a_1= -2 | - | - |
| 1 | a_(1+1)=5a_1+2( 1) ⇕ a_2=5a_1+2( 1) |
a_2=5 a_1+2 ⇓ a_2=5( -2)+2 |
a_2= -8 |
| 2 | a_(2+1)=5a_2+2( 2) ⇕ a_3=5a_2+2( 2) |
a_3=5 a_2+4 ⇓ a_3=5( -8)+4 |
a_3= -36 |
| 3 | a_(3+1)=5a_3+2( 3) ⇕ a_4=5a_3+2( 3) |
a_4=5 a_3+6 ⇓ a_4=5( -36)+6 |
a_4= -174 |
| 4 | a_(4+1)=5a_4+2( 4) ⇕ a_5=5a_4+2( 4) |
a_5=5 a_4+8 ⇓ a_5=5( -174)+8 |
a_5= -862 |
The first five terms of the sequence are -2, -8, -36, -174, and -862.