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Saturday, March 2, 2024

2024/017) integrate sin ax cos bx

We have \sin \, ax + \cos \, bx = \frac{1}{2} (\sin (a+b) x + \sin (a-b) x

Knowing that 

\frac{d}{dx} \ cos \, nx = - n \sin \, nx

Hence \int  (\sin \, ax  \cos \, bx) dx  = \int (\frac{1}{2} (\sin (a+b) x + \sin (a-b) x)dx  

= \frac{\cos(a+b)x}{a+b} - \frac{\cos(a-b)x}{a-b} + C  


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