What kind of lever is an axle

The essence of wheel axle is that it can rotate lever continuously. When using wheel axle, generally, the action lines of forces acting on wheel and shaft are tangent to wheel and shaft, so their force arms are corresponding wheel radius and shaft radius

How to prove the formula of 1 / F = 1 / V + 1 / u in convex lens imaging

Proof by similar triangle

What is the imaging law formula of convex lens?

Convex lens imaging law refers to the object placed outside the focus, on the other side of the convex lens inverted real image, there are three kinds of real image reduction, equal size, amplification. The smaller the object distance, the larger the image distance, the larger the real image. The object placed in the focus, on the same side of the convex lens upright enlarged virtual image. The smaller the object distance, the smaller the image distance, the smaller the virtual image
Please refer to:

Imaging formula of concave convex mirror imaging formula of concave convex lens
It's best to have an explanation

When light passes through a convex lens, it is refracted only once in the middle (here at the y-axis). Note: X (red) axis - main optical axis of convex lens, y (blue) axis - convex lens o - optical center, F - focal length, u - object distance, V - image distance, a - object length, purple line - passing through optical center

The imaging formula of convex lens 1 / F = 1 / U + 1 / V, f is "focal length", u is "object distance", V is "distance"

As shown in the figure, the light from the real object AB passing through the focus F2 parallel to the main optical axis and the light passing through the lens center intersects with the point E, then De is the real image, Bo is the object distance u, do is the image distance v. from the similar triangle, Bo / OD = AB / de Co / de = of 2 / F 2D can be obtained, and ab = CO can be obtained from the rectangular aboc, so of 2 / F 2D = & nbsp

A geometry proof in junior high school
Known: triangle ABC, D is the midpoint of BC, ∠ B = 2 ∠ C, BC = 2Ab. Prove: Triangle abd is equilateral triangle

Make the bisector of angle B intersect AC with E and connect de. from ASA axiom, it can be proved that EBD is equal to ECD and angle EDB is 90 degrees; from SAS axiom, it can be proved that EBA is equal to EBD and angle Bae is 90 degrees; it can be calculated that angle abd is 60 degrees

For a general triangle, if one inner angle is twice that of the other, it is called double angle triangle. In double angle triangle ABC, three sides are ABC, and angle a is twice that of angle B. how to prove that a * a = B (B + C)

See the attached figure: it can be proved that BD is the bisector of angle CBE
So DG = DM
Because D is the midpoint of the BC arc, point m is also the midpoint of BC
Therefore, DG / (BC / 2) = Tan 30 degrees
So DG = root 3
Annex: 6. GSP

How to do a good job in geometry proving in junior high school
To solve the problem of comprehensive proof, we need to use a little bit of everything,

I'm also a sophomore in junior high school, so I know I'll tell you some tips. Generally, the known conditions in the questions will be used. Generally, there are two big questions, the second one will use the answer of the first one. In addition, there is a kind of more difficult question type, which is that a certain paragraph is twice or half of a certain paragraph

A geometry proof problem in junior high school,
For those straight lines passing through an intersection of two intersecting circles, of the line segments cut by two circles, the one parallel to the connecting line is the longest,

Note: the centers of two circles are m and N respectively; the intersection point is a and B. make a straight line L through a point to intersect two circles. Now make MC perpendicular to L through M, perpendicular to C through N, perpendicular to L through N, perpendicular to D through n. analysis: MC and Nd bisect the chord of L cut by circle respectively, so chord length = 2 times CD to connect Mn, angle MND = a, then CD = Mn * sin (a) chord length = 2 * Mn * sin (...)

Seek several master often make mistakes, but it is the foundation of junior high school geometry proof problem
Ordinary people generally do not make mistakes, but experts often make mistakes
Not necessarily --
Most of the experts don't care about the details. They use the extracurricular theorem directly, but the textbook doesn't, so the teacher makes mistakes-
For example --

Proof of theorem
Proof of definition
Most inferential proof masters often make mistakes

What kind of lever is an axle