Understanding of geometric meaning of partial derivative It is said in the book: let M0 (x0, Y0, f (x0, Y0)) be a point on the surface z = f (x, y), pass M0 to make the plane y = Y0, cut the surface to get a curve, and the equation of the curve on the plane y = Y0 is Z = f (x, Y0), then the partial derivative FX (x0, Y0) is the slope of the tangent m0tx of the curve on the X axis at the point M0 When I look at the picture, it looks like a tangent to the x-axis, which is not easy to understand

Derivative represents the rate of change, which reflects the speed of the dependent variable changing with the independent variable
In one variable function, k = Lim △ Y / △ X
When we calculate the partial derivative of a function of two variables to x, we fix y = Y0 to see the rate of change of Z with X
So in the plane y = Y0,
K = Lim △ Z / △ x, which is the slope of the curve to the x-axis

How do you know how much magnification a magnifying glass is
For example, I bought a magnifying glass, but it didn't say how many times of magnification. How do I know this is my less times of magnification? And how does a microscope know how many times of magnification this is
There are no explanations. But if there are explanations, how are they defined

When the object to be observed is placed outside the focus of the objective lens and close to the focus, the real image formed behind the objective lens is just inside the focus of the eyepiece and close to the focus, which is magnified into a virtual image again by the eyepiece

A right triangle knows how to calculate the length of a side by an angle

Right triangle knows that angle can't calculate side length, and it needs one side length to calculate other side lengths by trigonometric function

How does the subject change when it is the third person singular, present and predicate

That's the general rule
1. Generally, add - s at the end of the word, pronounce it as [S] after the clear consonant, and pronounce it as [Z] after the voiced consonant and vowel
Verb third singular: help (help), play (plays)
2. For words ending with s, x, CH, SH, add - es at the end of the word. The original word has e at the end. Generally, only - s is added, which means [iz]
Verb third person singular: wash (washes), close (closes)
3. Words ending with a consonant letter plus - y, first change y to I, then add - es, read as [iz]
Verb third person singular: fly (flies), study (Studies)

Please tell me what are obtuse triangle, orthogonal triangle and Rui angle triangle respectively

If one of the three angles of a triangle is an obtuse angle, that is, an angle greater than 90 degrees, it is called an obtuse triangle; if one angle is a right angle, that is, an angle equal to 90 degrees, it is called a right triangle; if all three angles are acute angles, that is, an angle less than 90 degrees, it is called an acute triangle
In a triangle, only one angle can be a right angle or an obtuse angle

Will the original form of "used to" followed by "get used to" followed by "ing" never change
There will be an English test tomorrow,

Used to do is to do something in the past
Get used to doing is similar to be used to doing

Understand the profound impact of the development of science and technology on human society

Science and technology is a decisive force to promote the development of history. The history of science and technology is not only the history of human cognition of nature and the world, but also the history of human wisdom. The 20th century is a century of brilliant achievements in science and technology, and also a century of increasingly mature human rationality

In the front of the classroom is our teacher

No, it can be written like "the woman / man who standing in the front of the classroom is our teacher." there are other ways to write it. If you need to ask, I hope you can help

As shown in the figure, in △ ABC, ab = AC, extend BC to D, make CD = BC, CE ⊥ BD, intersect ad to e, connect be, intersect AC to point F, verify: AF = FC

It is proved that: take the midpoint h of BC, connect ah, ∵ AB = AC, ∵ ah ⊥ BC ∵ CE ⊥ BD, ∥ ah ∥ EC, ∵ CD = BC ∥ CD = 2CH ∥ de = 2ae, take the midpoint m of ED, connect cm ∵ CE ⊥ BD, ∥ m as the midpoint of ED, ∵ me = AE ∵ C as the midpoint of BD, ∥ cm ∥ be, ∥ F as the midpoint of AC, AF = FC

sports

sports show
Network
Sports program; sports program; sports performance
Bilingual examples
1.People from all over the world were watching the greatest sports show of the Olympic Games.
People from all over the world are watching the largest sports performance the Olympic Games
2.I'm not much of an athlete,but I enjoy watching sports show.\x09
I'm not much of an athlete, but I like to watch performances
3.Description :2 nd graders of FDPS performed folk dance at the 2001 Sports Show.\x09
The second year students of fudge primary school performed the boy dance in the 2001 sports performance
4.Those boys always show off their sports skills to the girls.\x09
The boys are always showing off their sports skills to the girls