if f be decreasing continuous function satisfying f(x+y)=f(x)+f(y)-f(x)f(y) and x,ybelong to R,, f'(0)= -1 then , integrating f(x) 0--->1 dx =
if f be decreasing continuous function satisfying f(x+y)=f(x)+f(y)-f(x)f(y) and x,ybelong to R,, f'(0)= -1 then , integrating f(x) 0--->1 dx =