Question

what is the vaule of a1 for a geometric sequence with a4 =40 and a6 =160?

Answer 1

Find a5 first by taking Geometric Mean:

\[\large a_5 = \sqrt{a_4 \times a_6} = a_5 = \sqrt{40 \times 160} = a_5 = 80\]

Answer 2

Now find r:

\[r = \frac{a_5}{a_4} = \frac{80}{40} = 2\]

Answer 3

thank you

Answer 4

So:

Third term will be: 40/2 = 20

Second term will be : 20/2 = 10

And first term will be : 10/2 = 5.

\(\color{green}{\textbf{First Term is : 5..}}\)