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4.06 Infinite geometric series

Interactive practice questions

Consider the infinite sequence $1$1, $x-7$x7, $\left(x-7\right)^2$(x7)2, $\left(x-7\right)^3$(x7)3, $\ldots$

Complete the gaps to determine for what range of values of $x$x the infinite series has a limiting sum.

$\editable{}<1\andword x-7>\editable{}$<1andx7>

Solution:

$x<\editable{}\andword x>\editable{}$x<andx>

Medium
2min

Determine the limiting sum of the infinite series $\frac{1}{5}+\frac{3}{5^2}+\frac{1}{5^3}+\frac{3}{5^4}+\frac{1}{5^5}+\text{. . . }$15+352+153+354+155+. . .

Hard
4min

Consider the infinite geometric sequence: $72$72, $-24$24, $8$8, $-\frac{8}{3}$83, $\ldots$

Medium
2min

For a particular geometric sequence, $t_1=7$t1=7 and $S_{\infty}=\frac{35}{4}$S=354.

Medium
3min
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Outcomes

1.5.1.5

establish and use the formula S_∞=(t_1)/(1-r) for the sum to infinity of a geometric progression

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