To make the image of the projector bigger, we must make the convex lens close to the object and the projector away from the screen So, why do you do this? Keep the projector away from the screen, why change the image distance?

1. As the object distance increases, the distance decreases and the image shrinks
2. Away from the screen
There is a convex lens on the projector. If the projector is far away from the screen, it is equivalent to increasing the distance between the convex lens and the light screen

To physics master to tell the meaning of each letter in these formulas! There are all the formulas of high school one compulsory one, thank you! Give points
△X=X2-X1 △t=t2-t1 V=△X/△t a=△V/△t △V=V-V0 V=V0+at X=V0T+1/2at²
V & # 178; - V0 = 2aX average velocity V (that is, there is a cross on V) = (V0 + V1) / 2 △ x = at & # 178; V1 = GT
h=1/2gt² V1²=2gh

Looking at these formulas on the computer, I always think that they are strange and can't be used for nothing. Right? Let me explain it. A certain distance is distance 2 minus distance 1 △ t = t2-t1, a certain time is time 2 minus time 1V = △ X / △ T, and the speed is that distance divided by that time a = △ V / △ t plus

The last three digits of a five digit number are 999. If the number can be divided by 23, what is the minimum number of five digits?

Let two digits be m, then m999 can be divisible by 23, 1000m + 999 = 43 × 23m + 11m + 43 × 23 + 10 = (43 × 23m + 43 × 23) + (11m + 10) can get (43 × 23m + 43 × 23) + (11m + 10) can be divisible by 23; because 43 × 23m + 43 × 23 can be divisible by 23, so 11m + 10 can be divisible by 23; suppose 11m + 10 = 23n, then M = (22n-11) △ 11 + (n + 1) △ 11, obviously n + 1 is divisible by 11, the minimum n is 10, and the minimum m is: (23 × 1) To sum up, the minimum number of five digits is 20999. A: the minimum number of five digits is 20999

The odd function f (x) defined on R satisfies f (x + 1) = - f (x). If f (1.5) = 1, then f (2010.5)=

The odd function is f (x) = - f (- x), and f (x) = - f (x + 1) = - (- f (x + 1 + 1)) = f (x + 2), so the function is a periodic function with a period of 2, f (2010.5) = f (2010.5-2012) = f (- 1.5) = - f (1.5) = - 1

A and B travel from a and B at the same time. B's speed is two-thirds of a's. after they meet, they continue to move. When a arrives at B and B arrives at a, they return immediately. It is known that the place where they meet is 20 kilometers away from the place where they first meet. How many kilometers are a and B?

The speed ratio is 1:2 / 3 = 3:2
The first time we met, Party A and Party B had a whole journey
Among them, 3 / (3 + 2) = 3 / 5 of the whole process
The distance between the first meeting point and a is 3 / 5 of the whole distance
The second meeting, a total of three full line
Among them, a had 3 × 3 / 5 = 9 / 5 whole courses
The distance between the second meeting point and a is 2-9 / 5 = 1 / 5 of the whole course
The distance between two meeting points is 3 / 5-1 / 5 = 2 / 5 of the whole course
AB distance: 20 △ 2 / 5 = 50 km

The centroid properties of triangles
How to determine the center of gravity of a triangle? The relationship between the center of gravity and the three sides? And other relationships?

1) The center of gravity is divided into two parts, and their length ratio is 2:1.2. The three center lines divide the triangle into six small pieces, and the area of the six small pieces is equal. That is to say, the line between the center of gravity and the three vertices divides the area of the triangle into three equal parts

It is known that ABC belongs to R, a + B + C = 1. It is proved that 1 of a plus 1 of B plus 1 of C is greater than or equal to 9

Left = [a + B + C] / (a) + [a + B + C] / (b) + [a + B + C] / (c)
=3＋[(a/b)＋(b/a)]＋[(c/a)＋(a/c)]＋[(c/b)＋(b/c)]
The basic inequality is used in every bracket, and the result is: the left is greater than or equal to 3 + 2 + 2 + 2 = 9

In calculus, what is the left and right derivative? What is the specific definition?

Left derivative: if LIM (x → a -) (f (x) - f (a)) / (x-a) exists, the limit value is called the left derivative of F (x) at x = a. the definition of right derivative is similar

There are four teachers in our school who teach one class of mathematics in each of the four classes of a certain grade. When a mathematics test is conducted, each teacher is required not to invigilate in his own class. The invigilating methods are ()
A. 8 species B. 9 species C. 10 species D. 11 species

When there are no restrictions on invigilation, there are 24 ways to arrange invigilation, among which one person invigilates in the class with c41.2 = 8, two persons invigilate in the class with C42 = 6, and four persons invigilate in the class with 1, then there are 8 + 6 + 1 = 15 Ways to arrange invigilation that do not conform to the meaning of the topic; so there are 24-15 = 9 ways to arrange invigilation that conform to the meaning of the topic; so choose B

Finding the differential of function y = x Λ 2 * e Λ x

Solution
dy/dx=2x*e^x+x²e^x=(2x+x²)e^x
The differential is;
dy=[(2x+x²)e^x]dx

To make the image of the projector bigger, we must make the convex lens close to the object and the projector away from the screen So, why do you do this? Keep the projector away from the screen, why change the image distance?