The explicit rule for a sequence is an=7(−4)n−1

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What is the recursive rule for the sequence?


an=−4(an−1),a1=7
an=−7(an−1),a1=4
an=−7(an+1),a1=4
an=−4(an+1),a1=7

Respuesta :

The correct answer is

[tex]a_n=-4(a_{n-1}), a_1=7[/tex]

The explicit formula is of the form
[tex]a_n=a_1(r)^{n-1}[/tex], 
where a₁ is the first term and r is the common ratio.  Comparing this to our explicit form, we see that r = -4 and a₁ = 7.

The recursive formula is of the form
[tex]a_n=a_{n-1}*r[/tex]; using r=-4 gives us
[tex]a_n=-4(a_{n-1}), a_1=7[/tex]

Answer:

Option (a) is correct.

The recursive rule for the given sequence [tex]a_n=7(-4)^{n-1}[/tex] is [tex]a_n = (-4)\cdot a_{n-1}[/tex] with [tex]a_1=7[/tex]

Step-by-step explanation:

The explicit sequence of the geometric sequence is given by:

[tex]a_n = a_1r^{n-1}[/tex]  

where,  

[tex]a_1[/tex] is the first term

r is the common ratio  

n is the number of terms

For the given explicit rule, [tex]a_n=7(-4)^{n-1}[/tex]

Comparing with above sequence , we have,

[tex]a_1=7[/tex] and r = -4

Recursive formula for the geometric sequence having [tex]a_1=7[/tex] and r = -4  is given by:

[tex]a_n=r\cdot a_{n-1} \ for\ n\geq 2[/tex]

Putting values, we get,

[tex]a_n = (-4)\cdot a_{n-1}[/tex]

Hence, the recursive rule for the given sequence [tex]a_n=7(-4)^{n-1}[/tex] is [tex]a_n = (-4)\cdot a_{n-1}[/tex] with [tex]a_1=7[/tex]

hence, option (a) is correct.