Crack the Code: Unraveling the 8th Term of a Geometric Sequence

What is the 8th term of the geometric sequence: -9, 36, -144, 576, -2304, 9216, -36864?

• A. 172, 896
• B. 147, 456
• C. 128, 512
• D. 99, 461

Answer: (B)

To determine the 8th term of a geometric sequence, it is essential to identify the common ratio. In this sequence, the first term is -9, and each subsequent term is obtained by multiplying the previous term by the common ratio. To find the common ratio, divide the second term by the first term: 36 ÷ -9 = -4. Thus, the common ratio is -4. This means each term is -4 times the previous term. Now, we can calculate the 8th term of the sequence. The nth term in a geometric sequence can be found using the formula: \[ a_n = a_1 \cdot r^{(n-1)} \] where \(a_n\) is the nth term, \(a_1\) is the first term, \(r\) is the common ratio, and \(n\) is the term number. For this sequence: - First term (\(a_1\)) = -9 - Common ratio (\(r\)) = -4 - Term number (\(n\)) = 8 Substituting these values into the formula gives: \[ a_8 = -9 \cdot (-4

When you're preparing for the Florida Teacher Certification Examinations (FTCE) Subject Area Test, you’ll encounter all sorts of engaging questions. Some may leave you scratching your head, while others will make the math light bulb flicker on. Ever wondered how to determine the 8th term of a geometric sequence, such as -9, 36, -144, and so on? Well, let’s break it down in a way that makes perfect sense.

You know, geometric sequences can be a bit of a rollercoaster ride — they involve patterns that can seem a tad complex at first. But they’re really quite appealing once you grasp the concept. In our example, the first term is -9, and as you go down the line, each subsequent term just gets multiplied by a common ratio. And that’s the golden key to understanding them!

So, what’s the common ratio in our sequence? It’s as simple as dividing the second term by the first: (36 \div -9). What do we get? A delightful little -4. Yep, that means each term multiplies by -4 to reveal the next. As you can see, this can lead to a back-and-forth pattern of positive and negative numbers. Isn’t that wild?

Alright, let’s pull out our magic formula, shall we? You’ll want to use the nth term formula:

[

a_n = a_1 \cdot r^{(n-1)}

]

Breaking that down: (a_n) stands for the nth term, (a_1) is the very first term (which is -9 in our case), (r) is the common ratio we just calculated (-4), and (n) represents the term number, which we want to find out for the 8th term.

Plugging it all in gives

[

a_8 = -9 \cdot (-4)^{7}

]

Yep, you heard right! We have to raise -4 to the power of 7 before multiplying it with -9. Now, if you’re already feeling a bit like your head is in a whirl, fear not! This is just a matter of arithmetic following the right steps.

Let’s break it down step by step.

First off, calculate (-4^{7}), which turns out to be -16,384. So next, multiply that by -9. Here’s where it feels like a magic trick: two negatives lead to a positive! Thus, (a_8 = 147,456).

And there you have it! The 8th term of your sequence is 147,456. Yes, not too shabby for some good, ol' math.

While preparing for the FTCE, it’s crucial to embrace these challenges. They’ll not only equip you with the skills needed to succeed on the test but also add to the plethora of knowledge you’ll pass on to future generations as a teacher. Remember, every little tidbit of math you tackle brings you one step closer to being that inspiring educator ready to light up young minds!

So, where does that leave you? With a newfound respect for geometric sequences, and perhaps a sense of accomplishment to boot. What's next on your study agenda? Keep at it, folks — you're doing great!