Pre-Calculus: Find a formula for the nth term: Given that a(4)=-12, & a(5)=-6

Question

noseboy908 · Answer

@Johnbc If you can help, please take a look.

anonymous · Answer

We have the 4th and 5th term so we can easily find the difference

anonymous · Answer

After we have the difference you can use the same method we used last problem to find the A1 term

noseboy908 · Answer

The difference would be 1/2

anonymous · Answer

$$A_n=A_1 + (n-1)d$$

anonymous · Answer

Yes it did go half or it also went +6

noseboy908 · Answer

I forgot to mention, but it's geometric. That's also given.

anonymous · Answer

Geometric Sequence$$A_n= A_1 \times r^{n-1}$$

noseboy908 · Answer

I believe I found the answer, I'll post the steps I used.

anonymous · Answer

|dw:1400808448617:dw| This should be similar to your steps?

noseboy908 · Answer

Root formula: t(n)=t(1) x r^(n-1)
                     -12=t(1) x (1/2)^(4-1)
                     -12=t(1)(.125)
                     -96=t(1)
So, the formula would be "t(n)=-96+(1/2)^(n-1)

anonymous · Answer

Correct!

noseboy908 · Answer

Alright, thanks again! I may be back with more momentarily.