It asks to prove that the integral [from 0 to pi] of e^t sin(t) = 1/2 (e^pi + 1)
By integrating by parts twice,
I don't get how since the bit after the integral in uv - integral v du
has e^t and some trig function. So how do we integrate that bit?
Thanks for any help
By integrating by parts twice,
I don't get how since the bit after the integral in uv - integral v du
has e^t and some trig function. So how do we integrate that bit?
Thanks for any help
-
just keep integrating by parts until you get an integral on the right that is the same as the one on the left.
int{u}dv = uv - int{v}du
u = e^t
du = e^tdt
dv = sin(t)dt
v = -cos(t)
int{e^tsin(t)}dt = -e^tcos(t) + int{cos(t)e^t}dt
u = e^t
du = e^tdt
dv = cos(t)dt
v = sin(t)
int{e^tsin(t)}dt = -e^tcos(t) + [e^tsin(t) - int{sin(t)e^t}dt]
move the int{sin(t)e^t}dt] on the right over to the left. Clever :)
2*int{e^tsin(t)}dt = -e^tcos(t) + e^tsin(t)
int{e^tsin(t)}dt = (1/2)(-e^tcos(t) + e^tsin(t))
int{e^tsin(t)}dt = (1/2)(e^t)(sin(t)-cos(t))
evaluate from 0 to pi
(1/2)[e^pi][sin(pi)-cos(pi)] - (1/2)(e^0)[sin(0)-cos(0)]
(1/2)e^pi - (1/2)(1)(-1)
(1/2)e^pi + 1/2
(1/2)(e^pi + 1)
int{u}dv = uv - int{v}du
u = e^t
du = e^tdt
dv = sin(t)dt
v = -cos(t)
int{e^tsin(t)}dt = -e^tcos(t) + int{cos(t)e^t}dt
u = e^t
du = e^tdt
dv = cos(t)dt
v = sin(t)
int{e^tsin(t)}dt = -e^tcos(t) + [e^tsin(t) - int{sin(t)e^t}dt]
move the int{sin(t)e^t}dt] on the right over to the left. Clever :)
2*int{e^tsin(t)}dt = -e^tcos(t) + e^tsin(t)
int{e^tsin(t)}dt = (1/2)(-e^tcos(t) + e^tsin(t))
int{e^tsin(t)}dt = (1/2)(e^t)(sin(t)-cos(t))
evaluate from 0 to pi
(1/2)[e^pi][sin(pi)-cos(pi)] - (1/2)(e^0)[sin(0)-cos(0)]
(1/2)e^pi - (1/2)(1)(-1)
(1/2)e^pi + 1/2
(1/2)(e^pi + 1)