Wednesday, 29 January 2014

integration - Compute intfrac1x(x2)(x+3) and intfraccos(3x)sin(3x)



Compute 1x(x2)(x+3) and cos(3x)sin(3x). I have no idea how to solve these 2 integrals, I've run out of ideas. The first one especially, I can't even start, not sure how to do it. I've done this for the second one:



I introduced a new variable t, 3x=t, therefore dx=dt3



Inserted into the integral: 13costsintdt, which leaves me with 13cot(t)dt and then it stops for me, I tried Per-Partes, but couldn't come up with anything useful.



How do I solve these 2 integrals? They're driving me nuts.


Answer




Hints : For the first one use partial fractions, noting that
1x(x2)(x+3)=15x104/5x+3.



For the second one there is an obvious change of variable.


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