The curve given by r(0) = cos(0) i + sin(0)3 + 20k for O E [0, 47] gives a helix (if you don't see why this is true, check the location of r(0) at 0 = 1/4, 71 / 2, 371 / 4, . ..). Then T' (0 ) N . J + and T ( 1 / 2 ) = N. 1 + + K Now find the length L of the helix. Then I2 / 2