Geometric Sequences help - (3 given terms, find the rest)

[jaxx]

I need to find the value of the first term for this geometric series.

Sn = 33
tn = 48
r = -2

I know that I have to take the formulas tn = t1 x r^(n-1), and Sn = [t1 x (r^n) - 1] / (r - 1), and isolate t1 for the first formula and then input that into the second, but I don't know the actual process of doing that.

If anyone can explain it step by step and with reasons maybe, that would be really helpful, I'm not good at math and get confused easily. Any help is appreciated

 

[stapel]

I know that I have to take the formulas tn = t1 x r^(n-1), and Sn = [t1 x (r^n) - 1] / (r - 1), and isolate t1 for the first formula and then input that into the second, but I don't know the actual process of doing that.

At what point in the process are you getting stuck? You've plugged the given values into the given formulas, and... then what?

Please reply showing your algebra so far. Thank you!

 

[jaxx]

I get 33 = t1[1 - (-2)^n] / 3.

I multiply both sides by 3 to get

99 = t1 [1 - (-2)^n].

From there I'm not entirely sure what to do to start simplifying. Can I subtract that 1, or do I have to divide by it? And how to I put the remaining (-2)^n on the left side of the equation, or at least isolate t1?

Thanks for the response

 

[stapel]

I get 33 = t1[1 - (-2)^n] / 3.

I multiply both sides by 3 to get

99 = t1 [1 - (-2)^n].

What are you doing with the other equation? You need both equations in order to be able to solve the exercise.