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alexandr1967 [171]
3 years ago
10

Use lagrange multipliers to find the points on the given surface that are closest to the origin. y2 = 64 + xz

Mathematics
1 answer:
Inessa [10]3 years ago
8 0
The distance between an arbitrary point on the surface and the origin is

d(x,y,z)=\sqrt{x^2+y^2+z^2}

Recall that for differentiable functions g(x) and h(x), the composition g(h(x)) attains extrema at the same points that h(x) does, so we can consider an augmented distance function

D(x,y,z)=x^2+y^2+z^2

The Lagrangian would then be

L(x,y,z,\lambda)=x^2+y^2+z^2+\lambda(y^2-64-xz)

We have partial derivatives

\begin{cases}L_x=2x-\lambda z\\L_y=2y+2y\lambda\\L_z=2z-\lambda x\\L_\lambda=y^2-64-xz\end{cases}

Set each partial derivative to 0 and solve the system to find the critical points.

From the second equation it follows that either y=0 or \lambda=-1. In the first case we arrive at a contradiction (I'll leave establishing that to you). If \lambda=-1, then we have

\begin{cases}2x+z=0\\2z+x=0\end{cases}\implies x=0,z=0

This means y^2=64\implies y=\pm8

so that the points on the surface closest to the origin are (0,\pm8,0).
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Two lighthouses are located 75 miles from one another on a north-south line. If a boat is spotted S 40o E from the northern ligh
yuradex [85]

Answer:

The northern lighthouse is approximately 24.4\; \rm mi closer to the boat than the southern lighthouse.

Step-by-step explanation:

Refer to the diagram attached. Denote the northern lighthouse as \rm N, the southern lighthouse as \rm S, and the boat as \rm B. These three points would form a triangle.

It is given that two of the angles of this triangle measure 40^{\circ} (northern lighthouse, \angle {\rm N}) and 21^{\circ} (southern lighthouse \angle {\rm S}), respectively. The three angles of any triangle add up to 180^{\circ}. Therefore, the third angle of this triangle would measure 180^{\circ} - (40^{\circ} + 21^{\circ}) = 119^{\circ} (boat \angle {\rm B}.)

It is also given that the length between the two lighthouses (length of \rm NS) is 75\; \rm mi.

By the law of sine, the length of a side in a given triangle would be proportional to the angle opposite to that side. For example, in the triangle in this question, \angle {\rm B} is opposite to side \rm NS, whereas \angle {\rm S} is opposite to side {\rm NB}. Therefore:

\begin{aligned} \frac{\text{length of NS}}{\sin(\angle {\rm B})} = \frac{\text{length of NB}}{\sin(\angle {\rm S})} \end{aligned}.

Substitute in the known measurements:

\begin{aligned} \frac{75\; \rm mi}{\sin(119^{\circ})} = \frac{\text{length of NB}}{\sin(21^{\circ})} \end{aligned}.

Rearrange and solve for the length of \rm NB:

\begin{aligned} & \text{length of NB} \\ =\; & (75\; \rm mi) \times \frac{\sin(21^{\circ})}{\sin(119^{\circ})} \\ \approx\; & 30.73\; \rm mi\end{aligned}.

(Round to at least one more decimal places than the values in the choices.)

Likewise, with \angle {\rm N} is opposite to side {\rm SB}, the following would also hold:

\begin{aligned} \frac{\text{length of NS}}{\sin(\angle {\rm B})} = \frac{\text{length of SB}}{\sin(\angle {\rm N})} \end{aligned}.

\begin{aligned} \frac{75\; \rm mi}{\sin(119^{\circ})} = \frac{\text{length of SB}}{\sin(40^{\circ})} \end{aligned}.

\begin{aligned} & \text{length of SB} \\ =\; & (75\; \rm mi) \times \frac{\sin(40^{\circ})}{\sin(119^{\circ})} \\ \approx\; & 55.12\; \rm mi\end{aligned}.

In other words, the distance between the northern lighthouse and the boat is approximately 30.73\; \rm mi, whereas the distance between the southern lighthouse and the boat is approximately 55.12\; \rm mi. Hence the conclusion.

4 0
2 years ago
Give the equation for a circle with the given center and radius.Center at (-10, -4), radius = 5A. (x−10)^2+(y−4)^2=25B. (x−4)^2+
BaLLatris [955]

D)(x+10)^2+(y+4)^2=5^2=25

Explanation

Step 1

We know that the general equation for a circle is

\begin{gathered} (x-h)^2+(y-k)^2=r^2 \\  \end{gathered}

where

(h,k) is the center of the circel

and r is the radius

then, all we need to do is replace

Let

\begin{gathered} \text{center}\Rightarrow(h,k)\Rightarrow(-10,-4) \\ \text{radius}\Rightarrow r\Rightarrow5 \end{gathered}

replace the values

\begin{gathered} (x-h)^2+(y-k)^2=r^2 \\ (x-(-10))^2+(y-(-4))^2=5^2 \\ (x+10)^2+(y+4)^2=5^2=25 \end{gathered}

therefore, the answer is

D)(x+10)^2+(y+4)^2=5^2=25

I hope this helps you

7 0
1 year ago
How many square feet of outdoor carpet will we need for this hole?
nadezda [96]

Answer:

45 square feet

Step-by-step explanation:

5 0
3 years ago
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A city map uses a scale in which 2.5 centimeters represents 3 kilometers. The distance on the map between the post office and th
marishachu [46]

Answer:

10.8 kilometers

6 0
2 years ago
3x - 5y = -16
murzikaleks [220]
X=3 y=5 hope this helped :)
4 0
3 years ago
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