Find the area of the surface.
The part of the sphere
x2 + y2 + z2 = 81
that lies above the plane
z = 4.

Parameterize this surface by

r (u, v) = 9 cos(u) sin(v) i + 9 sin(u) sin(v) j + 9 cos(v) k

with 0 ≤ u ≤ 2π and 0 ≤ v ≤ arccos(4/9)

See the attached sketch to see how we arrive at the upper limit for v.

Take the normal vector to the surface to be

n = ∂r/∂u × ∂r/∂v

n =  -81 cos(u) sin²(v) i -  81 sin(u) sin²(v) j - 81 sin(v) cos(v) k

which has magnitude

||n|| = 81 sin(v)

Then the surface area is

[tex]\displaystyle \iint_S \|\mathbf n\| \,\mathrm du\,\mathrm dv = 81 \int_0^{2\pi} \int_0^{\arccos(4/9)} \sin(v)\,\mathrm dv\,\mathrm du \\\\ = 162\pi \int_0^{\arccos(4/9)} \sin(v)\,\mathrm dv \\\\ = -162\pi (\cos\left(\arccos\left(\frac49\right) - \cos(0)\right) \\\\ = 162\pi \left(1 - \dfrac49\right) \\\\ = \boxed{90\pi}[/tex]

If you're not familiar with surface integrals, you can instead use what's sometimes called the projection method. Let

z = f(x, y) = √(81 - x ² - y ²)

(where we take the positive square root because we're looking at a part of the top half of the sphere)

Projecting the surface down onto the (x, y)-plane, we see that it casts a "shadow" of a disk with radius √(9² - 4²) = √65. (Use the Pythagorean theorem to solve for the missing side of the triangle in the sketch.)

Then the surface S considered above is hovering over the set in the (x, y)-plane,

D = {(x, y) : x ² + y ² ≤ 65}

The area is then

[tex]\displaystyle \iint_D \sqrt{1 + \left(\dfrac{\partial f}{\partial x}\right)^2 + \left(\dfrac{\partial f}{\partial y}\right)^2} \,\mathrm dx\,\mathrm dy[/tex]

It's easier to compute this integral in polar coordinates, so we take

x = r cos(t )

y = r sin(t )

dx dy = r dr dt

and the region D is given by the set

{(r, t ) : 0 ≤ r ≤ √65 and 0 ≤ t ≤ 2π}

Then the integral would be

[tex]\displaystyle \iint_D \sqrt{1 + \left(\dfrac{\partial f}{\partial x}\right)^2 + \left(\dfrac{\partial f}{\partial y}\right)^2} \,\mathrm dx\,\mathrm dy = \iint_D \sqrt{1 + \frac{x^2+y^2}{81-x^2-y^2}}\,\mathrm dx\,\mathrm dy \\\\ = \iint_D \sqrt{\frac{81}{81-x^2-y^2}}\,\mathrm dx\,\mathrm dy \\\\ = \int_0^{2\pi} \int_0^{\sqrt{65}} r \sqrt{\frac{81}{81-r^2}}\,\mathrm dr\,\mathrm dt[/tex]

Substitute s = 81 - r ² and ds = -2r dr :

[tex]\displaystyle \int_0^{2\pi} \int_0^{\sqrt{65}} r \sqrt{\frac{81}{81-r^2}}\,\mathrm dr\,\mathrm dt = 2\pi \int_0^{\sqrt{65}} r \sqrt{\frac{81}{81-r^2}}\,\mathrm dr \\\\ = -9\pi \int_{81}^{16} \frac{\mathrm ds}{\sqrt s} \\\\ = 9\pi \int_{16}^{81} s^{-1/2}\,\mathrm ds \\\\ = 18\pi \left(\sqrt{81} - \sqrt{16}\right) \\\\ = \boxed{90\pi}[/tex]

solve the inequality. graph your solution
6(y+1)>6

Please , I need help ASAP !!

Does anybody know this???

. The temperature fell 13°c on each of the first 2 days of the week. It rose 7°c on each of
the next 3 days and fell 9°c on each of the last 2 days. If the temperature was originally
34% what was the final temperature?

rectangular equation for the curve whose parametric equations are x = 2cosθ, y = cos2θ.

VI. PRACTICE TASKS
OSOBE
Practice Task 1
Directions: Place the decimal point to make each product correct.
1. 6.75
X 0.18
1215
2. 11.28
X 0.36
40608
3.10.15
X 0.15
15225
4.
1.15
X 0.25
02875
5.
3.22
X 1.12
39284

Pleassse answer this pleassssee

please help me for my practice problems​

Find an equation for the graph below

I don't understand this!!!

A relation R exists such that for every input (x ), the output is −x . Which statement about the relation R is correct?

Which is the following is a possible solution for the inequality? x+7<10

Mr. Candy needs to purchase large bags of Snickers to sell in the school store. A bag of Snickers contains 72 Snicker bars. A bag of Snickers cost $23. How much should Mr. Candy sell the Snicker bars to make a profit of $49?

simplify:
[tex]x ^{4} - {x}^{2} {y}^{2} + {y}^{4} [/tex]
x4-x2y2+y4​

If Marie were to paint her living room alone, it would take 7 hours. Her sister Barbara could do the job in 8 hours. How many hours would it take them working together? Express your answer as a fraction reduced to lowest terms, if needed.

What’s the answer to this H(-3)=3/4(8x+2)-4.5

Plz help I need help

16. What is the total number of different eight-letter arrangements that can be formed
using the letters in the word “SAVANNAH"?

:) Answer fast if you can

12/16•4/3 divided by 5/6

Pleas answer this question!

8+2x-4=6+2(x+1) please help

need help with this algebra ii question

Assume that y varies inversely as x. If
Y
y = 10 when
=
x = 4, what is the value for y when
x = 6?

How do i solve this?????

Help! Pls...........

Solve for the unknown angles

Marking you the brainliest​ provided you got it
right and with step by step explanation
​

A water tank is a cube of side 2m the depth of the water in it is 60cm. What is the volume of the water in the tank?

The pH scale measures how acidic or basic a substance is. Bleach is said to have a
55 POINTS!!! WILL MARK!!! ANSWER FAST!!!pH of less than 14 and greater than 11. Model the normal range of pH values of bleach, using a compound inequality.

11 > x > 14
11 < x < 14
11 ≤ x ≤ 14
11 ≥ x ≥ 14

-3x-5y=-7
Find slope of perpendicular line

Distance from earth to the moon is 238,900 . From earth to the sun is 92935,700 ,about how many times the distance from earth to the moon is distance from earth to the sun