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If `(10)^9 + 2(11)^1 (10)^8 + 3(11)^2 (10)^7+...........+10 (11)^9= k (10)^9` , then k is equal to :A. 100B. 110C. `(121)/(10)`D. `(441)/(100)` |
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Answer» Correct Answer - A Let `S=(10)^(9)+2(11)^(1)(10)^(8)+3(11)^(2)(10)^(7)+ . . . .+10(11)^(9)`. Then, `(11)/(10)S=11(10)^(8)+2(11)^(2)(10)^(7)+ . . . .+9(11)^(9)+(11)^(10)` `:." "S-(11)/(10)S=10^(9)+{(11)(10)^(8)+(11)^(2)(10)^(7)+ . . .+(11)^(9)}-(11)^(10)` `rArr-(S)/(10)=(10^(9){1-((11)/(10))^(10)})/(1-(11)/(10))-(11)^(10)` `rArr-(S)/(10)=-10^(10){1-((11)/(10))^(10)}-(11)^(10)` `rArr" "S=10^(11)-10(11)^(10)+10(11)^(10)=10^(11)=100(10^(9))` `rArr" "k(10^(9))=100(10^(9))rArrk=100` |
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