Give positive numbers a, b and c are such that ab + bc + ca + abc = 4, What is the value of 1/a+2 + 1/b+2 + 1/c+2 = ?
ab + bc + ca + abc = 4 is true only when a = b = c = 1 therefore 1/a+2 + 1/b+2 + 1/c+2 = 1/3 + 1/3 + 1/3 = 1.