1.

श्रेणी `1+2r+3r^(2)+4r^(3)+...`अनन्त पदों का योग `(9)/(16)`है ,तो r का मान ज्ञात कीजिए |

Answer» माना `" "S=1+2r+3r^(2)+4^(3)+..oo तक `
`rArr" "rS=r+2r^(2)+3r^(3)...oo`तक
`rArr " "(1-s)S=1+r+r^(2)+...oo तक =(1)/(1-r)`
`:. " "S=(1)/((1-r)^(2))`
दिया है : `" "S=(9)/(16)`
`:. " "(1)/((1-r)^(2))=(19)/(16)`
`rArr " "(1)/(r^(2)-2r+1)=(9)/(16)`
`rArr " "9r^(2)-18r-7=0`
`:. " "r=(7)/(3),(-1)/(3)`


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