Given that the function f [x] = x square + [A-3] x-3a... A is a constant, if A5, the solution of inequality negative f [x] is greater than 0

Given that the function f [x] = x square + [A-3] x-3a... A is a constant, if A5, the solution of inequality negative f [x] is greater than 0

f(x)=x²+(a-3)x-3a
=(x+a)(x-3)
-f(x)=-(x+a)(x-3)>0
be
(x + a) (x-3) - 3
-a

The solution of inequality about X: X & sup2; + (2a + 1) x-3a & sup2; - A

(x-a)(x+3a+1)-3a-1
a>-1/4
-3a-1

Let ABCD be a constant, if the solution set of inequality (B / x + a) + (x + D / x + C) < 0 is (- 1, - 1 / 3) U (1 / 2,1)
Then the solution set of inequality (BX / ax + 1) + (DX + 1 / CX + 1) < 0 is——

If f (x) = (B / x + a) + (x + D / x + C), then f (1 / x) = (BX / ax + 1) + (DX + 1 / CX + 1) f (x) < 0, the solution set is (- 1, - 1 / 3) ∪ (1 / 2,1) (BX / ax + 1) + (DX + 1 / CX + 1) < 0, that is, f (1 / x) < 0, then - 1 < 1 / x < - 1 / 3 or 1 / 2 < 1 / x < 1, then - 3 < x < - 1 or 1 < x < 2

A 1.8m long cuboid copper bar has a cross section of 5cm long square. If there is no cubic decimeter, the copper bar weighs 8.9kg, how much heavier is it than the copper bar?

5 cm = 0.5 decimeter
1.8 m = 18 decimeters
(0.5×0.5)×18×8.9
=0.25×18×8.9
=4.5×8.9
=40.05 (kg)

Using 2, 4, 6 and 3 to calculate 24 points, the comprehensive formula is ()
Using 2, 4, 6 and 3 to calculate 24 points, the comprehensive formula is ()

3*6+2+4
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Xiaoming did the experiment of "measuring resistance by voltammetry", including ammeter (range 0 ~ 0.6A, 0 ~ 3a), voltmeter (range 0 ~ 3V, 0 ~ 15V), sliding rheostat (resistance)
I want a detailed explanation
Xiaoming did the experiment of "measuring resistance by volt ampere method", including ammeter (range 0 ~ 0.6A, 0 ~ 3a), voltmeter (range 0 ~ 3V, 0 ~ 15V), sliding rheostat (resistance range 0 ~ 12 Ω), resistance R (6 Ω) and power supply composed of three new dry batteries in series. If the experiment requires that the pointer of the meter does not exceed its range, and the pointer of several measurements deviates from the middle line of the dial of the meter, the resistance of the rheostat connected to the circuit is at least ()
A。 1.5 Euro B. 2 Euro C. 2.5 euro D.3 Euro

It can be seen from the problem that the sliding rheostat is connected in series. The ammeter should choose 0-0.6 and the voltmeter 0-3. It can be seen from the circuit diagram that the sliding rheostat is connected with the current 0.3A ≤ I ≤ 0.6 and the voltage 1.8 ≤ V ≤ 2.7V, so the maximum resistance is 9 Ω and the minimum resistance is 3 Ω

How to prove that there is at least one prime number between N and 2n when n > 1

This theorem is called "Bertrand Chebyshev theorem"

In the series circuit, there are two resistors, R1 voltage is 4V, 10 ohm, the total current is 0.4A, R2 resistance
There is also a circuit B with a total voltage of 6V, which is a parallel circuit,

R2 = 0 Ω
In series circuit, the current is equal to 0.4A, R1 voltage is 4V, 10 ohm: R1 current is 0.4A; that is to say, when R2 = 0 ohm, it is true

Given that the parabola y ^ 2 = 8x, the chord AB passing through the point Q (1,1) is exactly bisected by Q, the equation of the line where AB is located is obtained

Let a (x1, Y1) B (X2, Y2) be solved and the linear AB equation be y = K (x-1) + 1
y1^2=8x1
y2^2=8x2
Subtraction of two formulas
(y1+y2)(y1-y2)=8(x1-x2)
k(y1+y2)=8
y1+y2=2
k=4
The linear AB equation is y = 4x-3

What effect does the coil resistance of relay have on relay? Is the greater the coil resistance, the better?

Let's talk about some basic background: the coil resistance is directly related to the number of turns. The number of turns and the current directly affect the electromagnetic attraction (it can be considered that the electromagnetic attraction is proportional to the product of the current and the number of turns). The electromagnetic attraction affects the stability of the relay. Generally, the coil resistance of similar relays with the same working voltage is similar, Because the working principle of the same kind of relay is similar. The required suction is the same
Back to your question, I said that the current and the number of turns affect your suction. Under the same diameter of enameled wire, the coil resistance directly determines the number of turns of your coil. The larger the resistance is, the smaller the passing current is. It's easy to understand that the larger the resistance is, the better. If the resistance is too large, the number of turns of the coil increases, but on the contrary, it will cause the flow current to be too small, and the product of the two will become smaller, In general, the resistance of relay is the best value after calculating the product of turns and current, that is, the product of turns and current is the largest
Therefore, the coil resistance is not the greater the better, but suitable!