You need to solve the integral `int (x-1) sin (pi*x) dx = int x*sin (pi*x) dx - int sin (pi*x)dx`
You need to use substitution `pi*x = t => pi*dx = dt => dx = (dt)/(pi)`
`int x*sin (pi*x) dx = 1/(pi^2) int t*sin t`
You need to use the integration by parts for `int t*sin t ` such that:
`int udv = uv - int vdu`
`u = t => du = dt`
`dv = sin t=> v = -cos t`
...
You need to solve the integral `int (x-1) sin (pi*x) dx = int x*sin (pi*x) dx - int sin (pi*x)dx`
You need to use substitution `pi*x = t => pi*dx = dt => dx = (dt)/(pi)`
`int x*sin (pi*x) dx = 1/(pi^2) int t*sin t`
You need to use the integration by parts for `int t*sin t ` such that:
`int udv = uv - int vdu`
`u = t => du = dt`
`dv = sin t=> v = -cos t`
` `
`int t*sin t = -t*cos t + int cos t dt`
`1/(pi^2) int t*sin t = 1/(pi^2)(-t*cos t + sin t) + c`
Replacing back the variable yields:
`int x*sin (pi*x) dx = 1/(pi^2)(-pi*x*cos(pi*x) + sin (pi*x)) + c`
`int (x-1) sin (pi*x) dx = 1/(pi^2)(-pi*x*cos(pi*x) + sin (pi*x))+ (cos (pi*x))/(pi) + c`
Hence, evaluating the integral, using integration by parts, yields `int (x-1) sin (pi*x) dx = 1/(pi^2)(-pi*x*cos(pi*x) + sin (pi*x))+ (cos (pi*x))/(pi) + c.`
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