Question

Calculate a7 for the geometric sequence with a1 = 4 and common ratio r=-2

Answer 1

The geometric sequence is given by the next formula:

`a_n=a_1(r)^(n-1)`

Where r represents the common ratio and n is the number for the sequence.

Now, we have the next given values:

r=-2

a1 =4

and we need to find a7, which means n=7.

Replacing on the geometric sequence formula:

`a_7=-4(-2)^(7-1)`
`a_7=-4(-2)^6`
`a_7=-256`

Then, the correct answer is option C.