Recycle Bin Posted December 27, 2016 Report Share Posted December 27, 2016 Reply Link to post Share on other sites More sharing options...
FChaosi_ Posted December 27, 2016 Report Share Posted December 27, 2016 u4/u1 = r^3 r^3 = [1/3]/[1/81] r^3 = 27 r = 3 Graph Sn using sum of a geometric series formula. Find Sn = 40 using graphics calculator. Given that Sn increases as n increases, round to the next n if needed. 1 1 Reply Link to post Share on other sites More sharing options...
Recycle Bin Posted December 27, 2016 Author Report Share Posted December 27, 2016 32 minutes ago, FChaosi_ said: u4/u1 = r^3 r^3 = [1/3]/[1/81] r^3 = 27 r = 3 Graph Sn using sum of a geometric series formula. Find Sn = 40 using graphics calculator. Given that Sn increases as n increases, round to the next n if needed. thank you! Reply Link to post Share on other sites More sharing options...
astonky Posted December 29, 2016 Report Share Posted December 29, 2016 Or for part (b) you can also start solving it algebraically: u1*rn = 40 (establish equation using the formula for geometric equations in the formula booklet) Rearrange the equation: rn = 40/u1 Substitute for u1: rn =40/(1/81) So: rn= 40*81 which is 3240 Using logarithms: log3 3240 = n On a non-calculator find out 3 to the power of what number is greater than 3240 using trial and error: eg. 35 = 243 36 = 729 37 = 2187 38 = 6561 On a calculator just use the log solver to find that n = 8 1 Reply Link to post Share on other sites More sharing options...
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