B how much wire should be used for the square in

(b) How much wire should be used for the square in order to minimize the total area?
$$29 √ 3 · (49+4 √ 3)
m
Solution or Explanation
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10. 13/13 points | Previous Answers SCalcET7 4.7.046.MI.SA.
This question has several parts that must be completed sequentially. If you skip a part of the question,
you will not receive any points for the skipped part, and you will not be able to come back to the skipped
part.
Tutorial Exercise
A boat leaves a dock at 8:00 PM and travels due south at a speed of 20 km/h. Another boat has been
heading due east at 15 km/h and reaches the same dock at 9:00 PM How many minutes after 8:00
were the two boats closest together?
Part 1 of 7
Let t be the time, in hours, after 8:00 PM If the position of the boat at t = 0 corresponds to the origin,
then the position of the boat heading south at time t is
PM

12/14/16, 3)50 PM hw24S4.7
Page 6 of 9
Part 2 of 7
The position of the boat heading east at time t is
Part 3 of 7
The distance D between the two boats is given by
Part 4 of 7
We will minimize
Part 5 of 7
We have
Part 6 of 7
Solving gives us which is a minimum since
Part 7 of 7
Round your answer to the nearest minute.
( x , y ) =
$$0
,
$$ − 20 t
.
( x , y ) = ( -15 -15 + 15 t , 0 0 ).
D = .
225 225 ( t − 1)
2
+ 400 400 t
2
f ( t ) = [
D ( t )]
2
= 225(
t − 1)
2
+ 400 t
2
= 625 625 t
2
− 450 450 t + 225 225 .
f ' ( t ) = 1250 1250 t − 450 450 .
0 = f ' ( t ) t = ,
450 450
1250
f '' ( t ) > 0.

12/14/16, 3)50 PM hw24S4.7
Page 7 of 9
The boats are closest together 22 22 minutes after 8:00 PM.
You have now completed the Master It.
11. 3/3 points | Previous Answers SCalcET7 4.7.047.
A man launches his boat from point A on a bank of a straight river, 3 km wide, and wants to reach point
B , 1 km downstream on the opposite bank, as quickly as possible (see the figure below). He could row
his boat directly across the river to point C and then run to B , or he could row directly to B , or he could
row to some point D between C and B and then run to B . If he can row 6 km/h and run 8 km/h, where
should he land to reach B as soon as possible? (We assume that the speed of the water is negligible