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| PAGE: 188 | SET: Exercises | PROBLEM: 48 |
Two people starts from the same point at 
.
One walks toward east with a speed of 
mi/h.
Other walks towards northeast with a speed of 
mi/h.
Therefore, 
and 
.
Assume after some time 
, first person reaches the point 
and other one reach the point 
.
Let the sides of the triangle be considered 
, 
and 
.
One person moves east and other one moves northeast means angle between them is 
.
Apply cosine rule to the 
.
.
Substitute 
in above expression.
Differentiate on each side with respect to .
Find the rate at which the change in the distance between them after 
minutes.
Distance travelled by the first person in 
minutes is 
mi.
Distance travelled by the second person in minutes is 
mi.
Find distance between the two persons after minutes:
Consider 
.
Substitute corresponding values in above expression.
Rate at which the change in the distance between them after minutes is 
.
Rate at which the change in the distance between them after minutes is .
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