How to calculate density in physics

How to calculate density in physics

Density = mass / volume
ρ=m/v

When a piece of a × B rectangular paper is folded into the side of a regular hexagonal prism (the bottom surface is a regular hexagon), the surface area of the regular hexagonal prism is

If B side is taken as the perimeter of the bottom surface, then the root of 12 is 3B square + ab
On the contrary, the positions of a and B are reversed

In Cartesian coordinates, the set of points on the coordinate axis can be expressed as ()
{（x,y)|xy=0}
Why?

Because at least one of the coordinates of a point on the coordinate axis is 0, the ordinate of a point on the X axis is 0, and the abscissa of a point on the Y axis is 0, xy = 0, so it is expressed as {(x, y) | xy = 0}

How much sand, stone, cement and C25 are needed for one cubic meter of concrete

C25 concrete, general cement: Sand: Gravel = 310:670:1180 (kg), different raw materials in different places, different amount of cement, the mix is for reference only

Let a > b > C > 0, then the minimum value of 2A2 + 1ab + 1a (a − b) - 10ac + 25c2 is______ ．

∵ a > b > C > 0, ∵ 2A2 + 1ab + 1a (a − b) - 10ac + 25c2 = A2 + 1B (a − b) + (a − 5C) 2 ≥ A2 + 1 (B + a − B2) 2 + (a − 5C) 2 = A2 + 4a2 + (a-5c) 2 ≥ 2A2 · 4a2 + 0 = 4. If and only if a = 2B = 5C = 2, take the equal sign. Therefore, the minimum value of 2A2 + 1ab + 1a (a − b) - 10ac + 25c2 is 4

1 mm = () micron = () nanometer

1 decimeter = (100000) microns,
1 cm = (10000) μ m,
1 mm = (1000) microns,
1m = (1000000000) nm,
1 decimeter = (100000000) nm,
1 cm = (10000000) nm,
1 mm = (1000000) nm,
1 μ M = (1000) nm,
1 nm = (0.001) μ m,

A physics problem about mass and density
The following statement is true
A. The density of a large object must be small
B. A dense object must have a large mass
C. A dense object has a large mass per unit volume
D. The density of a solid must be higher than that of a liquid
2 the density of human body is about equal to the density of water, then the volume of a middle school student is closest to the following value
A.0.005m³
B.0.05m³
C.0.5m³
D.5m³

1c.2b, let me know

The square of (x / 2-y / 2) - 1 / 4 (the square of X - what is the square of Y

Original formula = 1 / 4 (xsquare-2xy + ysquare) - 1 / 4 (xsquare-ysquare)
=1 / 4 (x square + y Square) - 2xy-1 / 4 (x square - y Square)
=1 / 2Y squared - 1 / 2XY
=-1/2Y(Y-X）

Tangent chord equation of circle
I mean, the general tangent chord equation is (x-a) 2 + (y-b) 2 = R2, not x2 + y2 = R2
The tangent point chord equation (if even this is better) or the tangent point chord instead of the common chord equation is not the tangent point equation, which means that the tangent line of a circle passing through a point outside the circle can definitely make two tangents, then the two tangents intersect at a and B points respectively. So what's the equation of line AB

If the circle is (x-a) ^ 2 + (y-b) ^ 2 = R ^ 2 and the point outside the circle is (s, t), then the equation of the tangent chord is
(A-S) x + (B-T) y = (a ^ 2 + B ^ 2-r ^ 2-as-bt), or
(s-a)(x-a)+(t-b)(y-b)=r^2.
Solution: according to the equation that the tangent point should satisfy ([tangent point - (s, t)] slope and [tangent point center] slope are negative reciprocal each other; tangent point is on the circle), two tangent points (whose complexity is far beyond imagination) are obtained, and then two-point formula is used
This is the most stupid way, also the most mechanical, can be completed by computer
Of course, it can also be done by root axis method
Another method is relatively simple: first, find the tangent chord of (S-A, T-B) about x ^ 2 + y ^ 2 = R ^ 2, and then (x-a, y-b) instead of (x, y)

The ratio of the total volume of cylinder to the volume of combustion chamber is called compression ratio. The compression ratio determines the gasoline grade of engine
twenty-five
The ratio of the total volume of the engine cylinder to the volume of the combustion chamber is called compression ratio. The compression ratio determines the grade of gasoline used in the engine. When the compression ratio is greater than 10.0, No. () gasoline is generally used
A
ninety
B
ninety-three
C
ninety-five
D
ninety-seven

Above D97