How to calculate the area of equilateral triangle The side length is 4cm computing method Is there only Pythagorean theorem emergency

How to calculate the area of equilateral triangle The side length is 4cm computing method Is there only Pythagorean theorem emergency

Bottom multiply height divide 2
Suggest you use Pythagorean, because it is relatively simple

Calculating the area of a triangle with unequal sides
The area of unequal triangle is 82.5 meters for side a, 67.5 meters for side B and 45.5 meters for width. What is the total square?

Half circumference P = (82.5 + 67.5 + 45.5) / 2 = 97.75
Area s = √ {P (P-A) (P-B) (P-C)}
= √{97.75*(97.75-82.5)*(97.75-67.5)*(97.75-45.5)}
= √{97.75*15.25*30.25*52.25}
≈ 1535

The area formula of regular triangle
I saw someone ask this question,
But there are several answers,
If a is the side length,
The answer is no:
Root of 12 times a square?

If a is the length of the side, then the area is three times the square of A
If a is the perimeter, then the area is three times a square of the root of 12

The area formula of regular triangle

A quarter root is three times a square

F = bil if the magnetic induction line is not perpendicular to the current direction, how to calculate the ampere force and its direction?

The magnetic induction line is decomposed into the magnetic induction line perpendicular to the current direction and the magnetic induction line in the same linear direction with the current direction. Since only the vertical one can cut the current wire, f = bil is the magnetic induction line strength perpendicular to the current direction!

Ampere force F = bil, what is IL?
What is the name of I * l?

Why is ampere force F = Bil and how to deduce it?

This is not a derived formula. This is the definition of magnetic induction B
B is equal to the magnitude of the magnetic field force on the conductor perpendicular to the direction of the magnetic field with a length of 1 m and a current of 1 A
Although the expression is b = f / IL, the definition is f = bil

How to deduce the magnetic field formula B = u0i / (2 π R) around an electrified straight wire

From Ampere's loop theorem
∫ B dl = μ0 Σi
Therefore, for a straight wire, take a circle with the wire as the center, and the magnetic induction intensity of each part of the circle is tangential
(explain here that the left end is the line integral of the magnetic induction, here is the circumference of the circle, and the right end is the algebraic sum of the current passing through the circle (Gaussian surface))
B*2πR=μ0 I
∴ B=μ0 I/(2πR)

The magnetic induction of a magnetic field produced by an electrified straight wire (not infinite length)

The non infinite length can be obtained by the above formula, i.e. Biot Savart's law

The magnetic field is related. On the side of an infinite and fixed electrified straight wire AB, there is a straight wire CD with a certain length that can move freely
On the side of the infinite and fixed electrified straight wire AB, there is a straight wire CD with a certain length that can move freely. There is a current I2 in it. AB and CD are in the same plane and perpendicular to each other, then ()
A. The CD will move up
B. The CD will move down
C. The C end moves up and the d end moves down
D. CD turns parallel to AB and the direction of current in AB is opposite
PS: where AB is placed vertically, the current flows from bottom to top; CD is placed horizontally, the current flows from left to right
The correct answer is ad
I know the reason for choosing A. why is D right?

Because the magnetic field produced by ab is opposite to that produced by Cd on the side of CD and is in the upper half, the end near ab of CD will repel each other, CD will tilt, and then chain reaction will occur. Finally, CD and ab are parallel, and the current direction is opposite