Given that x minus y equals 2, then the square of two parts of x plus the square of Y minus XY

Given that x minus y equals 2, then the square of two parts of x plus the square of Y minus XY

If the problem is: 1 / 2 (the square of X + the square of Y) - xy = 2

If a number is equal to its reciprocal, then the number is ()
A. 1b. - 1C. ± 1D. ± 1 and 0

∵ 1 × 1 = 1, (- 1) × (- 1) = 1, ∵ the number equal to its reciprocal is ± 1

Why is the molar mass m density p Avogadro constant n 1kg of a substance and the molecular number pN / m of the substance?
RT
The key is to understand why P is not m / M = n, and NN is not the number of molecules?

Amount of substance (moles) of 1kg of the substance
n = m/M = 1/M
The number of molecules contained is n * n = n / m
It's not about density! The answer is wrong!

a. B is a rational number. If a new operation "*" is defined, a * b = a × A-B + A-1, please calculate the following questions according to the definition of "*"
2*（-5）=2x2-（-5）+2-1
=4-（-5）+2-1
=4+5+2-1
=10
（1）3*6 （2） （1*3）*（-3）

(1) 5
(2) 2+(4/9)

There is a lamp with a voltage of 2.5 and a filament resistance of 5 Ω. There is a power supply with a voltage of 6V,
Then connect it with a resistance of Ω

If the voltage at both ends of the bulb is 2.5V and the resistance is 5 Ω, then the current flowing through the bulb is 2.5V △ 5 Ω = 0.5A. Because the circuit and the bulb are connected in series, the current in the series circuit is equal everywhere, we can know that the current flowing through the resistance is also 0.5A. Because of the series voltage division, then the voltage divided by the resistance is the total voltage U-U lamp = u resistance, That is, 6v-2.5v = 3.5V. According to Ohm's law, the resistance value of the resistance is U / I = 3.5A △ 0.5A = 7 Ω. Another method is: if the series circuit knows the current, the total resistance of the circuit can be obtained, then the total resistance of the circuit is 6 △ 0.5 = 12 Ω. The characteristic of the series circuit is that the total resistance is equal to the sum of the partial resistances, then the resistance value of the series resistance is equal to the total resistance minus the resistance of the filament, that is r total - R lamp = r = 12 Ω - 5 Ω = 7 Ω

(4×10³)³(-0.125×10²)=?

Original formula = - (64 × 10 ^ 9) × (0.125 × 10 & # 178;)
=-(64×0.125)×(10^9×10²)
=-8×10^11

Does a 1.5V dry cell with a resistance of 1 ohm generate a current of 1.5A? Why? What is the power of a normal dry cell?

Because the battery itself has internal resistance, it will be less than 1.5A

There is only one common point between the straight line L passing through P (0,1) and the hyperbola x ^ 2-y ^ 2 / 3 = 1
Is there a more detailed one? There is another one where a line is tangent to a common point

Let the equation of line l be Y-1 = KX = = = > y = KX + 1
(k²-3)x²+2kx+4=0
Δ = 4K & sup2; - 4 * 4 (K & sup2; - 3) = - 12K & sup2; + 48, let Δ = 0 = = = > k = ± 2
The equation of line L: y = 2x + 1 and y = - 2x + 1

Would you like to use 220 V voltage to connect 144 LED lights (white light-emitting diodes), 18 in a string, 8 in a string, and how much resistance do you need

18 in a string, 3 by 54 can be connected to the 220 V rectifier power supply, but the resistance to get (310-220 =) 90 V voltage, so we need to calculate the resistance value

Proof: hyperbola x ^ 2-15y ^ 2 = 15 and ellipse x ^ 2 of 25 + y ^ 2 of 9 have the same focus

Hyperbola x ^ 2-15y ^ 2 = 15
x^2/15-y^2=1
c^2=15+1=16
Focus F1 (- 4,0) F2 (4,0)
Ellipse x ^ 2 / 25 + y ^ 2 / 9 = 1
c^2=25-9=16
Focus F1 (- 4,0) F2 (4,0)
The hyperbola x ^ 2-15y ^ 2 = 15 has the same focus as the ellipse x ^ 2 / 25 + y ^ 2 / 9