?How do you find the sum of the infinite geometric series a1 = 27 and r = -4/5?

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Answer 1 · 2018-07-09T08:02:36

#15#

Sum #S_{\infty}# of infinite geometric progression (G.P.) with first term #a_1=27# & a common ratio #r=-4/5# is given as

#S_{\infty}=\frac{a_1}{1-r}#

#=\frac{27}{1-(-4/5)}#

#=\frac{27}{9/5}#

#=\frac{27\cdot 5}{9}#

#=3\cdot 5#

#=15#