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\begin{array}{rlr}D(t)^{2} & =A(t)^{2}+E(t)^{2} & \\ & =(4 t)^{2}+(3 t)^{2} & \\ & =16 t^{2}+9 t^{2} & \\ & =25 t^{2} & \\ D(t) & =\pm \sqrt{25 t^{2}} \qquad \qquad \text { Solve for } D(t) \text { using the square root. } \\ & =\pm 5|t| & \end{array}