※ 引述《nsr1290 (许喷)》之铭言：
: The coordinates of a particle in the xy-plane are differential
: function of time t with dx/dt=-1 m/sec dy/dt=-5 m/sec.
: How fast is particle's distance form the origin changing as it passes
from
: through the point(5 , 12)?
: Thank you!
R = √[x^2 + y^2]
x_0 = 5
y_0 = 12
dR/dt |
(5, 12)
= (xx' + yy')/R
= (-5 - 60)/13
= -5 (m/sec)