NIntegrate

NIntegrate[f,{x,xmin,xmax}] gives a numerical approximation to the integral ∫xminxmax f dx. 

NIntegrate[f,{x,xmin,xmax},{y,ymin,ymax},…] gives a numerical approximation to the multiple integral ∫xminxmaxdx∫yminymaxdy … f.

NIntegrate[f,{x,y,…}∈reg] integrates over the geometric region reg.

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