A formula for calculating the density of an object

A formula for calculating the density of an object

Density = mass / volume

How to calculate 99 × (9 / 11-3 / 8) + 3 / 8 × 99

99×（9/11-3/8)+3/8×99
=99×（9/11-3/8+3/8）
=99×9/11
=81

If the line passing through the focus intersects the parabola y ^ 2 = 2px (P > 0) at two points a and B, a (x1, Y1) B (X2, Y2)
If ad through a is perpendicular to the guide line D, BC through B is perpendicular to the guide line C, then ∠ DFC =?

This problem uses the definition of parabola
AF＝AD,BF=BC
∠AFD=∠ADF=1/2(180-∠FAD)
∠BFC=∠BCF=1/2(180-∠FBC)
Because of AD / / BC, ∠ fad + ∠ FBC = 180
∠AFD+∠BFC=1/2(360-∠FAD-∠FBC)=90
∠ DFC = 180-90 = 90 degrees

Compared with the volume of cylinder, cube and cuboid with equal base and height, ()
A. Cube is bigger B. cuboid is bigger C. cylinder is bigger D

Because the volume of cylinder, cube and cuboid can be calculated by the formula: v = sh, and the volume is the same because of equal base and height

56.8% 99.1% 400% 0.9%
56.8% 99.1% 400% 0.9% 175.65% 615% 1.49% 9000% convert percentage into decimal or integer

0.568
zero point nine nine one
four
zero point zero zero nine
one point seven five six five
six point one five
zero point zero one four nine
ninety

The proof of Lagrange's mean value theorem is continuous and invertible on (0,1), and there is at least one ξ such that f (x) '= 2 ξ (f (1) - f (0)) holds

Constructor g (x) = f (x) - (f (1) - f (0)) * x ^ 2, the mean value theorem can be applied to G (x)
In fact, it's the fastest way to use Cauchy's mean value theorem. Take g (x) = x ^ 2

An oxygen cylinder uses 1 / 5 of oxygen. How does the volume, mass and density change?

Constant volume: because oxygen is in the oxygen bottle, the gas has fluidity, and the change of molecular spacing is easier than that of solid and liquid. The gas will fill the closed container where it is. Its volume must be equal to the volume of the oxygen bottle, and the volume does not change. The mass decreases: because part of the oxygen is used, no matter how many parts are used, it is

Define a ⁃ B = 1-ab, divide a + B = is a kind of operation in the range of rational number, find the value of 2 ⁃ B (- 3)

=1-(-3+2)/(-3*2)
=1-5/6
=1/6

Who can explain the difference between double integral and triple integral (for example, what does double integral seek? What does triple integral seek? It's better to distinguish it in geometric sense)

What unit of length is 20 '?
What's the meaning of "20" in some instructions, like inches or feet?

20 'means foot
20 "for inch
Conversion to: 1foot = 12inch = 12 * 25.4mm