Find the value of limx→∞[x]+[2x]+[3x]+....[nx]n2 where [.] is an greatest integer function.
We have, limx→∞[x]+[2x]+[3x]+....[nx]n2
we know greatest integer of [x] lies between x-1 to x
x−1<[x]≤x ......(1)
Similarly
2x−1<[2x]≤2x .....(2)
3x−1<[3x]≤3x .....(3)
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nx−1<[nx]≤nx
Adding all these terms
We have,
x−1+2x−1+...nx−2<[x]+[2x]+.....[nx]≤x+2x+....nx
(x+2x+3x+...nx)−n<[x]+[2x]+.....[nx]≤x+2x+....nx
(1+2+3+...n)x−n<[x]+[2x]+[3x]+.....[nx]≤(1+2+3.....N)x
Sum of n terms ∑n=n(n+1)2
n(n+1)x2−n < [x]+[2x]+[3x]+...[nx] ≤ n(n+1)2.x