1.

r का मान ज्ञात कीजिए यदि- `1+2r+3r^(2)+4r^(3)+...oo तक=(25)/(16)` `2+5r+8r^(2)+11r^(3)+…oo तक=(35)/(12)`

Answer» Correct Answer - (i)`(1)/(5) (ii) (1)/(7)`
(i) `S_(oo)=(25)/(16)(दिया है)`
`S_(oo)=1+2r+3R^(2)+4r^(3)+….oo`
`rArr " "rS_(oo)=1.r+2r^(2)+3r^(3)+4r^(4)+…oo`
`rArr " "(1-r)S_(oo)=1+r+r^(2)+r^(3)+…oo=(1)/(1-r)`
`rArr " "S_(oo)=(1)/((1-r)^(2))=(25)/(16)`
`rArr " "(1-r)^(2)=(16)/(25) " "rArr " "1-r=(4)/(5)`
`rArr " "r=(1)/(5)`


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