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skelet666 [1.2K]
3 years ago
12

A hiker starting at point P on a straight road wants to reach a forest cabin that is 2 km from a point Q, 3 km down the road fro

m P . She can walk 8 km/hr along the road but only 3 km/hr through the forest. She wants to minimize the time required to reach the cabin. How far down the road should she walk before setting off through the forest straight for the cabin?

Mathematics
1 answer:
pantera1 [17]3 years ago
7 0

Answer:

2.19 km

Step-by-step explanation:

If x is the distance she walks down the road before turning, then the total time is:

t = x/8 + √((3 − x)² + 2²) / 3

t = x/8 + √(9 − 6x + x² + 4) / 3

24t = 3x + 8√(13 − 6x + x²)

24t = 3x + 8(13 − 6x + x²)^½

Take derivative of both sides with respect to x.

24 dt/dx = 3 + 4(13 − 6x + x²)^-½ (-6 + 2x)

When t is a minimum, dt/dx = 0.

0 = 3 + 4(13 − 6x + x²)^-½ (-6 + 2x)

-3 = 4(13 − 6x + x²)^-½ (-6 + 2x)

3 / (6 − 2x) = 4(13 − 6x + x²)^-½

3 / (24 − 8x) = (13 − 6x + x²)^-½

(24 − 8x) / 3 = (13 − 6x + x²)^½

(24 − 8x)² / 9 = 13 − 6x + x²

576 − 384x + 64x² = 117 − 54x + 9x²

459 − 330x + 55x² = 0

Solve with quadratic formula.

x = [ 330 ± √((-330)² − 4(55)(459)) ] / 2(55)

x = (330 ± √7920) / 110

x = 2.19 or 3.81

Since 0 < x < 3, x = 2.19.

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A car has a windshield wiper on the driver's side that has total arm length of 10 inches. It rotates
son4ous [18]

Answer:

75.44 Square Inches

Step-by-step explanation:

The diagram of the problem is produced and attached.

To determine the area of the cleaned sector:

Let the radius of the larger sector be R

Let the radius of the smaller sector be r

Area of the larger sector =\frac{\theta}{360}X\pi R^2

Area of the smaller sector =\frac{\theta}{360}X\pi r^2

Area of shaded part =Area of the larger sector-Area of the smaller sector

=\frac{\theta}{360}X\pi R^2-\frac{\theta}{360}X\pi r^2\\=\frac{\theta \pi}{360}X (R^2- r^2)

From the diagram, R=10 Inch, r=10-7=3 Inch, \theta=95^\circ

Therefore, Area of the sector cleaned

=\frac{95 \pi}{360}X (10^2- 3^2)\\=75.44$ Square Inches

7 0
3 years ago
True or False? The energy in a pendulum converts kinetic energy to potential energy, and then back again.
Karolina [17]
The answer to this question is true
4 0
2 years ago
Read 2 more answers
In psychology, there is a particular Mental Development Index (MDI) used in the study of infants. The scores on the MDI have app
ivann1987 [24]

Answer:

0.1587

Step-by-step explanation:

Here, mean=μ=100 and standard deviation=σ=16.

We have to find  P(average MDI scores of 64 children > 102)=P(xbar>102).

n=64

μxbar=μ=100

σxbar=σ/√n=16/√64=16/8=2

P(xbar>102)=P((xbar-μxbar)/σxbar>(102-100)/2)

P(xbar>102)=P(z>1)

P(xbar>102)=P(0<z<∞)-P(0<z<1)

P(xbar>102)=0.5-0.3413

P(xbar>102)=0.1587

Thus, the probability that the average is greater than 102 is 15.87%

4 0
3 years ago
A copy machine makes
IrinaK [193]
This problem can be represented in a formula with fractions. To make it more simple, we are converting 5m30s to just pure seconds, which = 154 copies in 330 seconds.

You set up the formula like this: 154/330 = x/60. (it is x/60 because you want to know the x amount of copies per 60 seconds)

Cross multiply, you get 330x = 9240. Divide both sides by 330, you get:

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The final answer is 28 copies per minute
7 0
3 years ago
Dharmesh has a square garden with a perimeter of 132 feet. Is the area of the garden greater than 1,000 square feet?
Delvig [45]

Answer: Yes. The area is 1089 square feet.

Step-by-step explanation:

For a square, all the sides are equal: L = W

Hence, the perimeter of a square = 4 × L

Perimeter = 4L

132 = 4L

132 ÷ 4 = L

33 = L = W

Area of a square with 33 feet sides = L × L = 33 × 33 = 1089

1089 > 1000

3 0
3 years ago
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