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Unformatted text preview: Math 23 B. Dodson Week 5: 13.3 arc length, curvature 13.4 velocity, acceleration; 14.1 functions of several variables Week 5 Homework: 13.3 curvature (Mon) Problem 13.3.16 Use formula (9) to find the curvature of r ( t ) = < t 2 , 2 t, ln t > . Solution: We start with part (a), find the unit tangent T and principal unit normal N . We compute r = < 2 t, 2 , 1 t > and  r  2 = 4 t 2 + 4 + 1 t 2 = (2 t + 1 t ) 2 , so  r  = 2 t + 1 t (since t > , is used for ln t ). 2 . We also simplify 1  r  = t 2 t 2 + 1 , then T = 1  r  r = t 2 t 2 + 1 < 2 t, 2 , 1 t > . Using the product rule, T = t 2 t 2 + 1 < 2 t, 2 , 1 t > + t 2 t 2 + 1 ( < 2 t, 2 , 1 t > ) = (2 t 2 + 1) t (4 t ) (2 t 2 + 1) 2 < 2 t, 2 , 1 t > + t 2 t 2 + 1 < 2 , , 1 t 2 > = 1 (2 t 2 + 1) 2 [( 2 t 2 + 1) < 2 t, 2 , 1 t > + t (2 t 2 + 1) < 2 , , 1 t 2 > ] = 1 (2 t 2 + 1) 2 < 4 t, 4 t 2 + 2 , 4 t > . To find the principal unit normal direction, we drop the (positive) scalar factor of 2 (2 t 2 + 1) 2 , and take the direction of...
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This note was uploaded on 02/29/2008 for the course MATH 23 taught by Professor Yukich during the Spring '06 term at Lehigh University .
 Spring '06
 YUKICH
 Arc Length

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