Recognize Problem: Recognize that the integral I=∫(lnx)2dx is not a standard integral and requires integration by parts.
Integration by Parts: Use integration by parts, which states that ∫udv=uv−∫vdu. Choose u=(lnx)2 (which we will differentiate) and dv=dx (which we will integrate).
Differentiate u: Differentiate u to find du. Since u=(lnx)2, we use the chain rule to find du=2(lnx)(1/x)dx=2(lnx)/xdx.
Integrate dv: Integrate dv to find v. Since dv=dx, we have v=x.
Apply Formula: Apply the integration by parts formula: ∫udv=uv−∫vdu. Substituting the chosen u, v, du, and dv, we get I=x(lnx)2−∫x(2(lnx)/x)dx.
Simplify Integral: Simplify the integral ∫x(x2(lnx))dx to ∫2(lnx)dx.
Recognize New Problem: Recognize that the integral ∫2(lnx)dx is another integration by parts problem. Choose u=lnx and dv=2dx.
Differentiate u: Differentiate u to find du. Since u=lnx, we have du=(x1)dx.
Integrate dv: Integrate dv to find v. Since dv=2dx, we have v=2x.
Apply Formula: Apply the integration by parts formula again: ∫udv=uv−∫vdu. Substituting the chosen u, v, du, and dv, we get ∫2(lnx)dx=2x(lnx)−∫x2xdx.
Simplify Integral: Simplify the integral ∫x2xdx to ∫2dx.
Integrate: Integrate ∫2dx to get 2x.
Combine Parts: Combine all parts to write the final expression for the original integral I. We have I=x(lnx)2−(2x(lnx)−2x)+C, where C is the constant of integration.
Final Expression: Simplify the expression to combine like terms. We have I=x(lnx)2−2x(lnx)+2x+C.
More problems from Find indefinite integrals using the substitution and by parts