To differentiate y=(lnx)cosx+(sinx)lnx, we will use logarithmic differentiation for each term separately, then add the results.
Let y=u+v, where u=(lnx)cosx and v=(sinx)lnx.
Then dxdy=dxdu+dxdv.
Step 1: Differentiate u=(lnx)cosx.
Take the natural logarithm of both sides:
lnu=ln((lnx)cosx)
Using the logarithm property ln(ab)=blna:
lnu=cosx⋅ln(lnx)
Now, differentiate both sides with respect to x using the product rule on the right side:
u1dxdu=dxd(cosx)⋅ln(lnx)+cosx⋅dxd(ln(lnx))
We know dxd(cosx)=−sinx.
For dxd(ln(lnx)), use the chain rule: dxd(lnf(x))=f(x)f′(x). Here f(x)=lnx, so f′(x)=x1.
dxd(ln(lnx))=lnx1⋅x1=xlnx1
Substitute these derivatives back:
u1dxdu=−sinx⋅ln(lnx)+cosx⋅xlnx1
Multiply by u to solve for dxdu:
dxdu=u(−sinx⋅ln(lnx)+xlnxcosx)
Substitute u=(lnx)cosx back:
dxdu=(lnx)cosx(−sinx⋅ln(lnx)+xlnxcosx)
Step 2: Differentiate v=(sinx)lnx.
Take the natural logarithm of both sides:
lnv=ln((sinx)lnx)
Using the logarithm property ln(ab)=blna:
lnv=lnx⋅ln(sinx)
Now, differentiate both sides with respect to x using the product rule on the right side:
v1dxdv=dxd(lnx)⋅ln(sinx)+lnx⋅dxd(ln(sinx))
We know dxd(lnx)=x1.
For dxd(ln(sinx)), use the chain rule:
dxd(ln(sinx))=sinx1⋅dxd(sinx)=sinx1⋅cosx=cotx
Substitute these derivatives back:
v1dxdv=x1⋅ln(sinx)+lnx⋅cotx
Multiply by v to solve for dxdv:
dxdv=v(xln(sinx)+lnx⋅cotx)
Substitute v=(sinx)lnx back:
dxdv=(sinx)lnx(xln(sinx)+lnx⋅cotx)
Step 3: Combine the derivatives.
dxdy=dxdu+dxdv
dxdy=(lnx)cosx(−sinx⋅ln(lnx)+xlnxcosx)+(sinx)lnx(xln(sinx)+lnx⋅cotx)
The final answer is (lnx)cosx(−sinx⋅ln(lnx)+xlnxcosx)+(sinx)lnx(xln(sinx)+lnx⋅cotx).
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