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Mathematics 10 Online
OpenStudy (anonymous):

Need serious help with integration by parts. Typing Question now.......

OpenStudy (anonymous):

\[\int\limits_{}^{} 64x ^{2}*\ln(x) dx\]

OpenStudy (anonymous):

I just cant seem to do integration by parts, if some can please help, that would be great.

OpenStudy (amistre64):

ln(x) should be your downward

OpenStudy (amistre64):

|dw:1316136517729:dw|

OpenStudy (amistre64):

\[\int{64x^2}{ln(x)}dx=\frac{64x^3}{3}ln(x)-\int\frac{64x^3}{3x}dx\]

OpenStudy (amistre64):

\[\int{64x^2}{ln(x)}dx=\frac{64x^3}{3}ln(x)-\int\frac{64x^3}{3x}dx\] \[=\frac{64x^3}{3}ln(x)-\int\frac{64x^2}{3}dx\] \[=\frac{64x^3}{3}ln(x)-\frac{64x^3}{9}+C\] maybe?

OpenStudy (amistre64):

\[=\frac{64x^3}{3}ln(x)-\frac{64x^3}{9}+C\] \[=\frac{64x^3}{9}(3ln(x)-1)+C\] is what the wolf shows

OpenStudy (anonymous):

i get the first term, but for the second i get (64/6)*x^2

OpenStudy (anonymous):

lol wolf is the man

OpenStudy (amistre64):

3*3 = 9, not 6

OpenStudy (amistre64):

\[\int udv=uv-\int vdu\] \[\begin{array}c u=ln(x)&du=\frac{1}{x}dx\\ dv=64x^2& v= \frac{64}{3}x^3 \end{array}\] \[\int ln(x)\ [64x^2\ dx]=ln(x)\ \frac{64}{3}x^3 -\int\frac{64}{3}x^3[\frac{1}{x} dx] \] \[\int ln(x)\ 64x^2\ dx=ln(x)\ \frac{64}{3}x^3 -\int\frac{64}{3}x^2 dx \] \[\int ln(x)\ 64x^2\ dx=ln(x)\ \frac{64}{3}x^3 -\frac{64}{3}\frac{1}{3}x^3 +C \]

OpenStudy (anonymous):

Hey i get it now. Calc makes my head hurt.

myininaya (myininaya):

recall product rule: \[(fg)'=f'g+fg'\] integrating both sides we get \[\int\limits_{}^{}(fg)' dx=\int\limits_{}^{}[f'g +fg'] dx=\int\limits_{}^{} f' g dx+\int\limits_{}^{} fg' dx\] so we have \[\int\limits_{}^{}(fg)' dx=\int\limits_{}^{}f' g dx+\int\limits_{}^{}f g' dx\] but \[\int\limits_{}^{}(fg)' dx=fg+C \] but for now we will just avoid the C and write \[\int\limits_{}^{}(fg)' dx=fg\] so we have \[fg=\int\limits_{}^{} f' g dx+\int\limits_{}^{} f g' dx\] now if we solve for \[\int\limits_{}^{}f'g dx\] we get the formula for integration by parts (you could have chose to solve the other one instead) \[\int\limits_{}^{}f' g dx=fg - \int\limits_{}^{}fg' dx\]

OpenStudy (anonymous):

|dw:1316137615394:dw| make a 7 and you have you integration by parts i remebered it by " across i multiply(x) and then i go across diagonal and down=-X(-multiplication)

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