7. In this problem, we prove that a straight line is the shortest curve between two points in Rd. Let p, q E Rd and let r be a curve such that r(to) = p and r(tı) = q, where to < t1. (a) Show that, if u is any unit vector in Rd, the r'(t) · u < ||r'(t)|| for all t. (b) Show that t1 (q - p) · u< / ||r(t)||dt. 1

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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7. In this problem, we prove that a straight line is the shortest curve between two points in
R. Let p, q E Rª and let r be a curve such that r(to) = p and r(t1) = q, where to < t1.
(a) Show that, if u is any unit vector in Rd, the r'(t) · u < ||r'(t)|| for all t.
• u
(b) Show that
(q – p) · u < / ||r (t)||dt.
to
1
(c) Show that the arc length of r from r(to) to r(t1) is at least ||q- p||. Hint: Consider
a well-chosen unit vector u.
Transcribed Image Text:7. In this problem, we prove that a straight line is the shortest curve between two points in R. Let p, q E Rª and let r be a curve such that r(to) = p and r(t1) = q, where to < t1. (a) Show that, if u is any unit vector in Rd, the r'(t) · u < ||r'(t)|| for all t. • u (b) Show that (q – p) · u < / ||r (t)||dt. to 1 (c) Show that the arc length of r from r(to) to r(t1) is at least ||q- p||. Hint: Consider a well-chosen unit vector u.
Expert Solution
Step 1

let p,qd and let r be a curve such that rt0=p and rt1=q where t0<t1

(a) show that, if u is any unit vector in d

r't·ur't for all t

(b) q-p·ut0t1r't dt

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