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.