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lim_(x rarr oo)int_(1)^(x)(ln t-(ln^(3)t)/(t))dt

limx1x(lntln3tt)dt \lim _{x \rightarrow \infty} \int_{1}^{x}\left(\ln t-\frac{\ln ^{3} t}{t}\right) d t

Full solution

Q. limx1x(lntln3tt)dt \lim _{x \rightarrow \infty} \int_{1}^{x}\left(\ln t-\frac{\ln ^{3} t}{t}\right) d t
  1. Split Integral: First, let's split the integral into two parts.\newline(lntln3tt)dt=lntdtln3ttdt\int(\ln t - \frac{\ln^3 t}{t}) dt = \int\ln t dt - \int\frac{\ln^3 t}{t} dt
  2. Antiderivative of lnt\ln t: Now, let's find the antiderivative of lnt\ln t.lntdt=tlntt+C\int \ln t \, dt = t \ln t - t + C
  3. Antiderivative of (ln3t)/t(\ln^3 t)/t: Next, we need to find the antiderivative of (ln3t)/t(\ln^3 t)/t. Let u=lntu = \ln t, then du=dt/tdu = dt/t. \int(\ln^\(3 t)/t \, dt = \int u^33 \, du = (u^44)/44 + C = (\ln^44 t)/44 + C
  4. Combine Antiderivatives: Combine the antiderivatives. (lntln3tt)dt=(tlntt)ln4t4+C\int(\ln t - \frac{\ln^3 t}{t}) dt = (t \ln t - t) - \frac{\ln^4 t}{4} + C
  5. Evaluate Definite Integral: Now, let's evaluate the definite integral from 11 to xx. 1x(lntln3tt)dt=[(xlnxx)ln4x4][(1ln11)ln414]\int_{1}^{x}(\ln t - \frac{\ln^3 t}{t}) dt = \left[(x \ln x - x) - \frac{\ln^4 x}{4}\right] - \left[(1 \ln 1 - 1) - \frac{\ln^4 1}{4}\right]
  6. Simplify Expression: Simplify the expression, noting that ln1=0\ln 1 = 0.1x(lntln3tt)dt=(xlnxx)ln4x4+1\int_{1}^{x}(\ln t - \frac{\ln^3 t}{t}) dt = (x \ln x - x) - \frac{\ln^4 x}{4} + 1
  7. Take Limit: Now, take the limit as xx approaches infinity. limx(xlnxx(ln4x)/4+1)\lim_{x \to \infty}(x \ln x - x - (\ln^4 x)/4 + 1)
  8. Take Limit: Now, take the limit as xx approaches infinity.limx(xlnxx(ln4x)/4+1)\lim_{x \to \infty}(x \ln x - x - (\ln^4 x)/4 + 1)As xx approaches infinity, xlnxx \ln x grows without bound, and so does x-x. However, the term (ln4x)/4(\ln^4 x)/4 grows much slower than xlnxx \ln x and x-x, so it becomes negligible.limx(xlnxx(ln4x)/4+1)=0+1\lim_{x \to \infty}(x \ln x - x - (\ln^4 x)/4 + 1) = \infty - \infty - 0 + 1

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