Let r: R-gt; R^3 be a curve in arc-length parametrization such that T(t) does not equal 0 for all t. Assume that the tangent line at any point r(t)...

Let r: R-> R^3 be a curve in arc-length parametrization such that T(t) does not equal 0 for all t. Assume that the tangent line at any point r(t) of the curve always passes through a point P. Show that r represents a straight line.