- #1
randoreds
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Ok I have to integrate -->∫cos(lnx) dx. could I use cos =U, -sinx=du, dv=lnxdx, v = 1/x
I know the difference technically, but in this situation it is kinda weird.
because the formula f(x)g(x)= uv-∫vdu. I thinking if they were number like 9(3) it would equal 27 so f(g) = f times G? but then that would mean ∫cos(lnx)dx = ∫cosxlnxdx . Which I don't think is right.
last guess: could you do cos(lnx)= U, -sinx(lnx) times (1/2) dx = du, DV = lnxdx, v =1/x
So I'm confused.
I asked by teacher, because my first taught was to do U-substituion then integrate by parts. She said that would work, but it would end up being a lot of ugly calculations. and that you could just integrate by parts directly. So if you could explain that, that would nice.
I know the difference technically, but in this situation it is kinda weird.
because the formula f(x)g(x)= uv-∫vdu. I thinking if they were number like 9(3) it would equal 27 so f(g) = f times G? but then that would mean ∫cos(lnx)dx = ∫cosxlnxdx . Which I don't think is right.
last guess: could you do cos(lnx)= U, -sinx(lnx) times (1/2) dx = du, DV = lnxdx, v =1/x
So I'm confused.
I asked by teacher, because my first taught was to do U-substituion then integrate by parts. She said that would work, but it would end up being a lot of ugly calculations. and that you could just integrate by parts directly. So if you could explain that, that would nice.
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