we are given with b(t) = [tex] \sqrt{ t^{2} + 4 } [/tex]. when b (t^2), we replace t inside the square root with t^2. Hence the equation becomes [tex] \sqrt{ t^{4} + 4 } [/tex]. The error in the answer given is not replacing t with t^2 and separating the terms inside the square root which should not be the case.
