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Integral of cos(x)*cos(kx) dx

Limits of integration:

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Piecewise:

The solution

You have entered [src]
 pi                   
  /                   
 |                    
 |  cos(x)*cos(k*x) dx
 |                    
/                     
0                     
$$\int\limits_{0}^{\pi} \cos{\left(x \right)} \cos{\left(k x \right)}\, dx$$
Integral(cos(x)*cos(k*x), (x, 0, pi))
The answer (Indefinite) [src]
                            //     2           2                                          \
                            ||x*cos (x)   x*sin (x)   cos(x)*sin(x)                       |
  /                         ||--------- + --------- + -------------  for Or(k = -1, k = 1)|
 |                          ||    2           2             2                             |
 | cos(x)*cos(k*x) dx = C + |<                                                            |
 |                          ||  cos(k*x)*sin(x)   k*cos(x)*sin(k*x)                       |
/                           ||- --------------- + -----------------        otherwise      |
                            ||            2                  2                            |
                            \\      -1 + k             -1 + k                             /
$${{\sin \left(\left(k+1\right)\,x\right)}\over{2\,\left(k+1\right)}} +{{\sin \left(\left(1-k\right)\,x\right)}\over{2\,\left(1-k\right)}}$$
The answer [src]
/     pi                             
|     --        for Or(k = -1, k = 1)
|     2                              
|                                    
<-k*sin(pi*k)                        
|-------------        otherwise      
|         2                          
|   -1 + k                           
\                                    
$$\begin{cases} \frac{\pi}{2} & \text{for}\: k = -1 \vee k = 1 \\- \frac{k \sin{\left(\pi k \right)}}{k^{2} - 1} & \text{otherwise} \end{cases}$$
=
=
/     pi                             
|     --        for Or(k = -1, k = 1)
|     2                              
|                                    
<-k*sin(pi*k)                        
|-------------        otherwise      
|         2                          
|   -1 + k                           
\                                    
$$\begin{cases} \frac{\pi}{2} & \text{for}\: k = -1 \vee k = 1 \\- \frac{k \sin{\left(\pi k \right)}}{k^{2} - 1} & \text{otherwise} \end{cases}$$

    Use the examples entering the upper and lower limits of integration.