# Double integral help

doubleIntegral( |cos(x+y)| dx dy ) over the rectangle [0, pi]x[0,pi]

I tried several ways to split the integral up so that I could remove the absolute value sign and integrate. However, I did not get the correct answer, so I must be splitting it wrong. Can someone show me how to split the region of integration up so I can integrate iteratively?

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At a glance, not saying this will work, but try using polar coordinates? ie x^2+Y^2=r^2 and so on.

Dick