The first three terms in a geometric progression are 144, x and 64 respectively, where x is positive. Find
- the value of x,
- the sum to infinity of the progression.
Solution
Given the first three terms of a geometric progression are 144, x, and 64.
Let the common ratio be r. Then:
\(x = 144r\)
\(64 = xr = 144r^2\)
Solving for r:
\(r^2 = \frac{64}{144} = \frac{4}{9}\)
\(r = \frac{2}{3}\)
Substitute r back to find x:
\(x = 144 \times \frac{2}{3} = 96\)
For the sum to infinity:
The formula for the sum to infinity of a geometric progression is:
\(S_\infty = \frac{a}{1 - r}\)
where a is the first term and r is the common ratio.
Substitute the values:
\(S_\infty = \frac{144}{1 - \frac{2}{3}} = \frac{144}{\frac{1}{3}} = 432\)
Log in to record attempts.