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01xlnxdx\int_{0}^{1}x \ln x\,dx

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Q. 01xlnxdx\int_{0}^{1}x \ln x\,dx
  1. Identify Problem: Identify the integral to be solved.\newlineWe need to evaluate the integral of xln(x)x \ln(x) with respect to xx from 00 to 11.
  2. Integration by Parts: Use integration by parts. Integration by parts formula is udv=uvvdu\int u \, dv = uv - \int v \, du. Let u=ln(x)u = \ln(x) and dv=xdxdv = x \, dx. Then we need to find dudu and vv.
  3. Find uu and vv: Differentiate uu and integrate dvdv.\newlineDifferentiating uu with respect to xx gives du=(1/x)dxdu = (1/x) dx.\newlineIntegrating dvdv with respect to xx gives v=(1/2)x2v = (1/2)x^2.
  4. Differentiate and Integrate: Apply the integration by parts formula.\newlineSubstitute uu, dudu, and vv into the integration by parts formula to get:\newlinexln(x)dx=(ln(x)(12)x2)((12)x2(1x)dx)\int x \ln(x) \, dx = (\ln(x) \cdot (\frac{1}{2})x^2) - \int((\frac{1}{2})x^2 \cdot (\frac{1}{x}) \, dx).
  5. Apply Integration by Parts: Simplify the integral.\newlineThe integral simplifies to (12)x2ln(x)(12)xdx(\frac{1}{2})x^2 \ln(x) - (\frac{1}{2})\int x \, dx.
  6. Simplify Integral: Evaluate the remaining integral.\newlineThe integral of xx with respect to xx is (12)x2(\frac{1}{2})x^2, so we have:\newline(12)x2ln(x)(14)x2(\frac{1}{2})x^2 \ln(x) - (\frac{1}{4})x^2.
  7. Evaluate Remaining Integral: Apply the limits of integration from 00 to 11. We need to evaluate (12)x2ln(x)(14)x2(\frac{1}{2})x^2 \ln(x) - (\frac{1}{4})x^2 from 00 to 11.
  8. Apply Limits of Integration: Evaluate the expression at the upper limit.\newlineWhen x=1x = 1, the expression becomes (12)(1)2ln(1)(14)(1)2=014=14(\frac{1}{2})(1)^2 \ln(1) - (\frac{1}{4})(1)^2 = 0 - \frac{1}{4} = -\frac{1}{4}.
  9. Evaluate Upper Limit: Evaluate the expression at the lower limit.\newlineWhen x=0x = 0, we encounter an indeterminate form 0×ln(0)0 \times \ln(0). However, we know that x2ln(x)x^2 \ln(x) approaches 00 as xx approaches 00 from the right. Therefore, the expression becomes 00.
  10. Evaluate Lower Limit: Subtract the value at the lower limit from the value at the upper limit.\newlineThe final value of the integral is 140=14-\frac{1}{4} - 0 = -\frac{1}{4}.

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