The integral from 1 to e^(pi/2) of the function: cos[ln(x)]dx
I know you need to integrate by parts, but I don't see how to on this one.
If you could show me how you got the answer that would be helpful
I know you need to integrate by parts, but I don't see how to on this one.
If you could show me how you got the answer that would be helpful
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∫ cos[ln(x)]dx from 1 to e^(π/2)
Let u = cos[ln(x)]
du = (-1/x)sin[ln(x)] dx
dv = dx
v = x
∫ cos[ln(x)]dx = xcos[ln(x)] + ∫sin[ln(x)] dx
Do it again:
u = sin[ln(x)]
du = (1/x)cos[ln(x)] dx
dv = dx
v = x
∫sin[ln(x)] dx = xsin[ln(x)] - ∫ cos[ln(x)] dx
So:
∫ cos[ln(x)]dx = xcos[ln(x)] + xsin[ln(x)] - ∫ cos[ln(x)] dx
Add the integral to both sides
2 ∫ cos[ln(x)]dx = xcos[ln(x)] + xsin[ln(x)]
∫ cos[ln(x)]dx = (1/2)xcos[ln(x)] + (1/2)xsin[ln(x)]
Now evaluate:
= (1/2)[e^(π/2)]cos[ln(e^(π/2))] + (1/2)[e^(π/2)]sin[ln(e^(π/2))] - (1/2)(1)cos[ln(1)] + (1/2)(1)sin[ln(1)]
= (1/2)[e^(π/2)]cos[π/2] + (1/2)[e^(π/2)]sin[π/2] - (1/2)cos[0] + (1/2)sin[0]
= (1/2)[e^(π/2)] - (1/2)
Done!
Let u = cos[ln(x)]
du = (-1/x)sin[ln(x)] dx
dv = dx
v = x
∫ cos[ln(x)]dx = xcos[ln(x)] + ∫sin[ln(x)] dx
Do it again:
u = sin[ln(x)]
du = (1/x)cos[ln(x)] dx
dv = dx
v = x
∫sin[ln(x)] dx = xsin[ln(x)] - ∫ cos[ln(x)] dx
So:
∫ cos[ln(x)]dx = xcos[ln(x)] + xsin[ln(x)] - ∫ cos[ln(x)] dx
Add the integral to both sides
2 ∫ cos[ln(x)]dx = xcos[ln(x)] + xsin[ln(x)]
∫ cos[ln(x)]dx = (1/2)xcos[ln(x)] + (1/2)xsin[ln(x)]
Now evaluate:
= (1/2)[e^(π/2)]cos[ln(e^(π/2))] + (1/2)[e^(π/2)]sin[ln(e^(π/2))] - (1/2)(1)cos[ln(1)] + (1/2)(1)sin[ln(1)]
= (1/2)[e^(π/2)]cos[π/2] + (1/2)[e^(π/2)]sin[π/2] - (1/2)cos[0] + (1/2)sin[0]
= (1/2)[e^(π/2)] - (1/2)
Done!