00:01
So it's given that you and a friend are riding your bikes to a restaurant that you think it is in east.
00:06
So and your friend thinks that restaurant is in north.
00:09
You both live from the same point.
00:10
So we are living from the same point.
00:12
With you riding at 16 miles per hour east.
00:15
So let's say one person is riding in this direction at speed of, let's say this is a distance or x dot since we are moving in the x direction.
00:27
16 miles per hour.
00:30
This can x dot nothing but dx by d t.
00:33
Now similarly your friend is riding as 12 miles per our north from the same point so let's have here which can be written as d y by dt since there is a vertical height change that is equals to 12 miles per hour.
00:47
Now we need to find after four miles so after a distance of four miles sorry it's minutes not mile so after t equals to four minutes we need to find at water it is a distance between you changing so we need to find this distance at water it is changing so let name this as x now since this is north and this is east it must be perpendicular now if you apply pythogamous let this length be y and this length be x after sorry let take this length as d so after time t we have length y, x and d.
01:26
So by pythagoras we'll have y square plus x square is equal to d square and we have to find rate of change of d so we'll differentiate this entire equation with time so we'll have 2 y, d y, d y, since y is changing with respect to time...