Respuesta :
Answer:
1.
Given the recursive formula:
[tex]a_3 = -11[/tex] and
[tex]a_n = 2a_{n-1} -1[/tex]
For n = 3:
[tex]a_3=2a_2 -1[/tex]
Substitute [tex]a_3 = -11[/tex] we have;
[tex]-11=2a_2 -1[/tex]
Add 1 to both sides we have;
[tex]-10 = 2a_2[/tex]
Divide both sides by 2 we have;
[tex]-5 = a_2[/tex]
or
[tex]a_2 = -5[/tex]
For n = 4, we have;
[tex]a_4=2a_3 -1[/tex]
Substitute [tex]a_3 = -11[/tex] we have;
[tex]a_4 = 2 \cdot -11 -1 = -22-1 = -23[/tex]
⇒[tex]a_4 = -23[/tex]
2.
Given:
[tex]a_4 = -36[/tex] and [tex]a_n = 2a_{n-1} -4[/tex]
For n = 4, we have;
[tex]a_4=2a_3 -4[/tex]
Substitute [tex]a_4 = -36[/tex] we have;
[tex]-36 = 2a_3 -4[/tex]
Add 4 to both sides we have;
[tex]-32 = 2a_3[/tex]
Divide both sides by 2 we have;
⇒[tex]a_3 =-16[/tex]
For n = 3:
[tex]a_3=2a_2 -4[/tex]
Substitute [tex]a_3 = -16[/tex] we have;
[tex]-16=2a_2 -4[/tex]
Add 4 to both sides we have;
[tex]-12 = 2a_2[/tex]
Divide both sides by 2 we have;
[tex]-6 =a_2[/tex]
or
⇒[tex]a_2 = -6[/tex]
The indicated terms of the sequence defined by each of the following recursive formulas are as follows:
- [tex]\mathbf{a_{2} = -5}[/tex]
- [tex]\mathbf{a_4 = -23}[/tex]
- [tex]\mathbf{{a_3}=-16}[/tex]
- [tex]\mathbf{{a_2}=-6}[/tex]
What are recursive formulas?
A recursive formula is one that describes each term in a series in terms of the term before it. The general term for an arithmetic sequence by using a recursive formula is [tex]\mathbf{a_n = a_{n-1} + d}[/tex]
From the given information:
- [tex]\mathbf{a_3 = -11}[/tex]
- [tex]\mathbf{a_n = -2a_{n-1} -1}[/tex]
Now, when n = 3
[tex]\mathbf{a_3 = -2a_{3-1} -1}[/tex]
[tex]\mathbf{-11= -2a_{2} -1}[/tex]
[tex]\mathbf{2a_{2} = -10}[/tex]
[tex]\mathbf{a_{2} = -5}[/tex]
When n = 4
[tex]\mathbf{a_4= -2a_{4-1} -1}[/tex]
[tex]\mathbf{a_4 = 2(-11) -1}[/tex]
[tex]\mathbf{a_4 = -23}[/tex]
Second Part:
- [tex]\mathbf{a_4 = -36}[/tex]
- [tex]\mathbf{a_n = 2_{an-1}-4}[/tex]
When n = 4
[tex]\mathbf{a_4 = 2_{a4-1}-4}[/tex]
[tex]\mathbf{a_4= 2_{a3}-4}[/tex]
[tex]\mathbf{-36+4= 2_{a_3}}[/tex]
[tex]\mathbf{2_{a_3}=-32}[/tex]
[tex]\mathbf{{a_3}=-16}[/tex]
When n = 3
[tex]\mathbf{a_3= 2_{a3-1}-4}[/tex]
[tex]\mathbf{a_3= 2_{a2}-4}[/tex]
[tex]\mathbf{-16= 2_{a_2}-4}[/tex]
[tex]\mathbf{2_{a_2}=-12}[/tex]
[tex]\mathbf{{a_2}=-6}[/tex]
Learn more about recursive formulas here:
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