Engineering
Mathematics
Integration by Parts
Integration of Miscellaneous Functions
Integration by Substitution
Question

The integral ∫cos(loge x )dx is equal to (where C is a constant of integration)

x[cos(loge x) + sin(loge x)] +C

x2[cos(logex)+sin(logex)]+C

x[cos(loge x) – sin(loge x)] +C

x2[sin(logex)−cos(logex)]+C

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Solution

I = ∫cos(lnx) dx = ∫1.cos(lnx) dx

∴I=x.coslnx+∫x · sinlnx · 1xdx

∴ I = x · cos (lnx) + ∫1.sin(ln x) dx

∴ I = x · cos (lnx) + x · sin x (lnx) −∫x · coslnx · 1x dx

∴ 2I = x (cos lnx + sin lnx)

∴I=x2(coslnx+sinlnx)+C