Question 1131037


 The formula for the general term for each geometric sequence is. Let's examine sequence A so that we can find a formula to express its nth term. 
The fixed number, called the common ratio ({{{r}}}); so, the formula will be 

{{{a[n] = a[1]*r^(n - 1) }}}

{{{-10}}}, {{{20}}}, {{{-40}}}, {{{80}}}, … 
{{{a[1]= -10}}}
{{{r=20/-10=-2}}}

{{{a[n] = -10*(-2)^(n - 1) }}}


check the rule:

if {{{n=4}}}

{{{a[4] = -10*(-2)^(4 - 1) }}}

{{{a[4] = -10*(-2)^3 }}}

{{{a[4] = -10*(-8) }}}

{{{a[4] = 80 }}}-> true, given fourth term of the sequence is {{{80}}}