Question

What is the value of y in the sequence below 2, У, 18,-54, 162

Answer 1

Answer:

y=-6

Step-by-step explanation:

Geometric Sequences

Any given sequence is said to be geometric if each term $a_n$ can be obtained as the previous term $a_{n-1}$ by a constant value called the common ratio.

$a_n=a_{n-1}.r$

or equivalently

$a_n=a_1.r^{n-1}$

Looking closely at the sequence 2, y, 18,-54, 162 we can try to find out if it's a geometric sequence or not. We compute the possible common ratios

$\displaystyle \frac{162}{-54},\ \frac{-54}{18}$ and we see they both result -3. If we use r=-3 and try to find the second term (y), then

y=2*(-3)=-6

Now we compute the third term: (-6)(-3)=18

Since we got the third term as given in the original sequence.

So y=-6