Hom Multivariable calc.. MY NOTES ASK YOUR TEACHER EXAMPLE 1 Find the length of the arc of the circular helix with vector equation r(t) = 2 cos(t) i + 2 sin(t) j + tk from the point (2, 0, 0) to the point (2, 0, 2x). SOLUTION Since r'(t) = we have |r' (t)1 = V (-2 sin(t) )2 + (2 cos(t) ) 2 + 12 = The arc from (2, 0, 0) to (2, 0, 27) is described by the parametric interval 0 S t S 2x and so, from this formula, we have . 2x L = [r'(t) | dt = dt