If \(a < b\) which of the following must be positive?
Explanation: এই problem টি সংখ্যা ধরে করলে কম সময়ে করা যায়। If \(a=1\) and \(b=2\), \(a^{2}-b^{2}=-3\) [(A) can be negative]. \(a^{3}-b^{2} = 1^{3}-2^{2} = 1-4 = -3\) [(C) can be negative]. If \(a=-2\) and \(b=-1\), \(b^{2}-a^{2} = (-1)^{2}-(-2)^{2} = 1-4 = -3\) [(B) can be negative]. \(b^{2}-ab = (-1)^{2}-(-2)(-1) = 1-2 = -1\) [(D) can be negative]. Therefore, none of them must be positive.
