anonymous 4 years ago math 12 geometric sequences. which term has the value of 7over1024 in the geometric sequence 28,14,7

1. Mimi_x3

It's like before; find the common ratio first.. $\large \frac{T_{2}}{T_{1}} = \frac{14}{28} = \frac{1}{2}$ $\large \frac{T_{3}}{T_{2}} = \frac{7}{14}=\frac{1}{2}$ Then use the formula.. $\large T_n = ar ^{n-1}$ where a is the first term of the sequence and r is the common ratio.. $\large T_n = \frac{7}{1024}$ $\large ar ^{n-1} = \frac{7}{1024}$

2. anonymous

yes I did that and i got 7 over 1024 = 28(1over2)to the power of n - 1

3. anonymous

and i divided each sides by 28

4. anonymous

and i used log method and I am not getting a right answer..

5. dumbcow

$(n-1) \log(\frac{1}{2}) = \log(\frac{7}{1024*28})$ $n-1 = 12$ n = 13

6. anonymous

ohhhhh okay thanks!!! :)