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Let f(n)= _ r=1 ^n ₁₀ ( 9 r+1 9 r-8 ) , then:

Options

  1. Af(11)=2
  2. Bf(11)=-2
  3. Cf(111)=3
  4. Df(1111)=4

Correct answer

D. f(1111)=4

Step-by-step solution

f(n)= _ r=1 ^n ( ₁₀(9 r+1)- ₁₀(9 r-8) ) f(n)= ₁₀(9 n+1) .

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