Integral of x*cos(x)^2 dx
The solution
Detail solution
-
Use integration by parts:
∫udv=uv−∫vdu
Let u(x)=x and let dv(x)=cos2(x).
Then du(x)=1.
To find v(x):
-
Rewrite the integrand:
cos2(x)=2cos(2x)+21
-
Integrate term-by-term:
-
The integral of a constant times a function is the constant times the integral of the function:
∫2cos(2x)dx=2∫cos(2x)dx
-
Let u=2x.
Then let du=2dx and substitute 2du:
∫4cos(u)du
-
The integral of a constant times a function is the constant times the integral of the function:
∫2cos(u)du=2∫cos(u)du
-
The integral of cosine is sine:
∫cos(u)du=sin(u)
So, the result is: 2sin(u)
Now substitute u back in:
2sin(2x)
So, the result is: 4sin(2x)
-
The integral of a constant is the constant times the variable of integration:
∫21dx=2x
The result is: 2x+4sin(2x)
Now evaluate the sub-integral.
-
Integrate term-by-term:
-
The integral of a constant times a function is the constant times the integral of the function:
∫2xdx=2∫xdx
-
The integral of xn is n+1xn+1 when n=−1:
∫xdx=2x2
So, the result is: 4x2
-
The integral of a constant times a function is the constant times the integral of the function:
∫4sin(2x)dx=4∫sin(2x)dx
-
There are multiple ways to do this integral.
Method #1
-
Let u=2x.
Then let du=2dx and substitute 2du:
∫4sin(u)du
-
The integral of a constant times a function is the constant times the integral of the function:
∫2sin(u)du=2∫sin(u)du
-
The integral of sine is negative cosine:
∫sin(u)du=−cos(u)
So, the result is: −2cos(u)
Now substitute u back in:
−2cos(2x)
Method #2
-
The integral of a constant times a function is the constant times the integral of the function:
∫2sin(x)cos(x)dx=2∫sin(x)cos(x)dx
-
There are multiple ways to do this integral.
Method #1
-
Let u=cos(x).
Then let du=−sin(x)dx and substitute −du:
-
The integral of a constant times a function is the constant times the integral of the function:
∫(−u)du=−∫udu
-
The integral of un is n+1un+1 when n=−1:
∫udu=2u2
So, the result is: −2u2
Now substitute u back in:
−2cos2(x)
Method #2
-
Let u=sin(x).
Then let du=cos(x)dx and substitute du:
-
The integral of un is n+1un+1 when n=−1:
∫udu=2u2
Now substitute u back in:
2sin2(x)
So, the result is: −cos2(x)
So, the result is: −8cos(2x)
The result is: 4x2−8cos(2x)
-
Now simplify:
4x2+4xsin(2x)+8cos(2x)
-
Add the constant of integration:
4x2+4xsin(2x)+8cos(2x)+constant
The answer is:
4x2+4xsin(2x)+8cos(2x)+constant
The answer (Indefinite)
[src]
/
| 2
| 2 x cos(2*x) /x sin(2*x)\
| x*cos (x) dx = C - -- + -------- + x*|- + --------|
| 4 8 \2 4 /
/
82xsin(2x)+cos(2x)+2x2
The graph
2 2
1 cos (1) sin (1) cos(1)*sin(1)
- - + ------- + ------- + -------------
4 2 4 2
82sin2+cos2+2−81
=
2 2
1 cos (1) sin (1) cos(1)*sin(1)
- - + ------- + ------- + -------------
4 2 4 2
−41+2cos2(1)+4sin2(1)+2sin(1)cos(1)
Use the examples entering the upper and lower limits of integration.