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In this question you must show all stages of your working - Edexcel - A-Level Maths Pure - Question 14 - 2022 - Paper 1

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In this question you must show all stages of your working. Solutions relying on calculator technology are not acceptable. Show that $$\int_{e}^{2} \frac{x^2}{4} \l... show full transcript

Worked Solution & Example Answer:In this question you must show all stages of your working - Edexcel - A-Level Maths Pure - Question 14 - 2022 - Paper 1

Step 1

Integrate by Parts

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Answer

Begin by using integration by parts, where we let:

u=lnxdu=1xdxu = \ln{x} \quad \Rightarrow \quad du = \frac{1}{x} \, dx dv=x24dxv=x312dv = \frac{x^2}{4} \, dx \quad \Rightarrow \quad v = \frac{x^3}{12}

Thus, x24lnxdx=x312lnxx3121xdx\int \frac{x^2}{4} \ln{x} \, dx = \frac{x^3}{12} \ln{x} - \int \frac{x^3}{12} \cdot \frac{1}{x} \, dx This simplifies to: x24lnxdx=x312lnx112x2dx\int \frac{x^2}{4} \ln{x} \, dx = \frac{x^3}{12} \ln{x} - \frac{1}{12} \int x^2 \, dx

Step 2

Evaluate the Remaining Integral

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Answer

Now, calculate the remaining integral:

x2dx=x33\int x^2 \, dx = \frac{x^3}{3}

Substituting this back, we have: x24lnxdx=x312lnx112x33+C\int \frac{x^2}{4} \ln{x} \, dx = \frac{x^3}{12} \ln{x} - \frac{1}{12} \cdot \frac{x^3}{3} + C Which simplifies to: x24lnxdx=x312lnxx336+C\int \frac{x^2}{4} \ln{x} \, dx = \frac{x^3}{12} \ln{x} - \frac{x^3}{36} + C

Step 3

Collect Terms

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Answer

Rearranging gives: x24lnxdx=x312lnx136x3+C\int \frac{x^2}{4} \ln{x} \, dx = \frac{x^3}{12} \ln{x} -\frac{1}{36} x^3 + C

To express it in the desired form: ax2+bax^2 + b Let:

  • a=112a = \frac{1}{12}
  • b=136b = -\frac{1}{36} thus, e2x24lnxdx=axe+b\int_{e}^{2} \frac{x^2}{4} \ln{x} \, dx = ax^e + b

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