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given that f(x) . f[f(x] = 1and f(1000) = 999hence for x = 1000 we have f(1000) . f [ f(1000) ] = 1 i.e. f(1000) f(999) = 1hence f (999) = 1/f(1000) = 1/999now since f is a continous functionit must attain all values between 1/999 and 999 in the interval [999,1000] since f(999) = 1/999 and f(1000) = 999hence for some x between 999 and 1000 the function will attain 500 such that f(x) = 500hence we have for that x f(x) . f[ f(x)] = 500 f(500) = 1hence f(500) = 1/500here u need not know the function but u can definitely say that f(500) = 1/500 since we are using the property of continous functions.
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