Dear all,
   I have a function f <- function(x,y,c){as.numeric(x*y < c) }
  I need to solve the value of c so that when I take the integral of
the function f from 0.2 to 0.8 with respect to x and from 0 to 1
with respect to y, the integral equal some prefixed value, say 0.025.
  It involves two dimension integration. Can anyone give some
help on this?
  Thank you so much in advance.
       Hannah

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