Answer:If \(a = 3\) and \(b = 4\) are the lengths of two sides of a rectangle, we cannot find \(c\) directly because the formula for the diagonal \(c\) in a rectangle involves the Pythagorean theorem:\[c = \sqrt{a^2 + b^2}\]Substituting the values:\[c = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5\]So, the diagonal \(c\) is 5 units.