If \(\int_0^n[x] \mathrm{dx}=66\), then \(n=\)

If \(\int_0^n[x] \mathrm{dx}=66\), then \(n=\)
  1. 24
  2. 9
  3. 12
  4. 7

Solution

\(\begin{aligned} & \int_0^n[x] d x=\int_0^1 0 d x+\int_1^2 1 d x+\int_2^3 2 d x+\ldots \ldots+ \\ & \int_{n-1}^n(n-1) d x \\ & =1+2+3+\ldots .+(n-1)=\frac{(n-1) n}{2}=66 \\ & \Rightarrow n(n-1)=132 \Rightarrow n=12 \end{aligned}\)

Asked in: BITSAT 2009

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