[three questions to fill in the blanks in the first year of junior high school] ① According to the requirements in brackets, the approximate number of 308.607 (accurate to one digit) is () ② If the complement of an angle is three times its remainder, then the angle is () ③ It is known that the speed of the ship in still water is a km / h, and the water speed is B km / h. The ship has sailed () km in total

1 309
2 45
3 3(a+b)+2(a-b)

(1) If 4x ^ 2-4x-3 = (2x + m) (2x + n), and M

m=-3,n=-1
m=3,n=2
m=11

How many watts per kilowatt hour is a 900 watt heater?

1 kwh = 1kws
0.9Kw * 1H = 0.9kwh

Normal number a, B and positive variable x, y satisfy a + B = 10, a / x + B / y = 1, minimum value of X + y = 18, find the value of a, B

It seems that we can't solve it by high school method. We need to use the derivative in higher mathematics

If a lamp of "220 V, 100 W" and B lamp of "220 V, 200 W" are connected in series into a 220 V circuit, then
(A) The ratio of resistance of two lamps RA ∶ RB = 2 ∶ 1
(B) The voltage ratio of the two lamps UA ∶ UB = 1 ∶ 2
(C) The ratio of electric power consumed by two lamps is pa ∶ Pb = 2 ∶ 1
(D) The ratio of heat released by two lamps at the same time is QA ∶ QB = 1 ∶ 2
(E) The ratio of current intensity in the two lamps is IA ∶ IB = 1 ∶ 1

A c e right

5.23 × 4 + 4.77 △ 0.25
1.95 △ 6 + 13.5 × 1.2

5.23×4+4.77÷0.25=5.23×4+4.77×4=4×（5.23+4.77）=4×10=40
If a number is divided by 0.25, it can be regarded as divided by a quarter, then it is equivalent to multiplying by 4, so~

The electromotive force of the power supply e = 24 V, internal resistance R = 1 Ω, resistance R = 2 Ω, M is DC motor, its armature resistance R = 1 Ω, when the motor works normally, the reading of voltmeter connected at both ends of the motor is UV = 21 V, so as to calculate the power of mechanical energy conversion of the motor
According to Ohm's law of closed circuit, e = UV + I (R + R), then:
According to the energy conservation, the mechanical power output of the motor is: P machine = Iuv – I2R / = (121 – 121) w = 20W
From Ohm's law of closed circuit: e = UV + I (R + R), isn't it true that E = IR + IR = I (R + R) can't be used for non pure resistance?

The symbol of internal resistance of power supply and armature resistance of motor should be separated. I will change the symbol of armature resistance to R1
In DC circuit, the motor is not pure resistance when it works
For the power supply and resistance R (the topic does not say the connection mode, I think it is in series), this part of the circuit can have
E＝I *R＋I *r＋Uv＝I*（R＋r）＋Uv
That is, 24 = I * (2 + 1) + 21
The current is I = 1 A
For the motor analysis, the input power is p input = I * UV = 1 * 21 = 21 watts
The power of armature heating is p heat = I ^ 2 * R1 = 1 ^ 2 * 1 = 1 watt
So the output power of the motor is p machine = P input-p heat = I * uv-i ^ 2 * R1 = 21-1 = 20 watts

Simple calculation 4.2-25 * 0.7 ÷ 5 4.7 * 2.34-0.34 * 4.7 28.7 * [0.54 ÷ (8.7 + 45.3)]

4.2-25*0.7÷5
=4.2-5*0.7
=4.2-3.5
=0.7
4.7*2.34-0.34*4.7
=4.7*（2.34-0.34）
=4.7*2
=9.4
28.7*[0.54÷（8.7+45.3）]
=28.7*[0.54÷54]
=28.7*0.01
=0.287

How is chemical energy transformed into electrical energy?

Chemical reaction is the process of gain and loss of electrons, a large number of electrons transfer into electric current, that is, chemical energy is converted into electric energy

Write an application problem of fractional equation, so that the unknown x satisfies the following fractional equation: two parts of X + three parts of X-2 = 1
You can read it. Come on,

If Party A and Party B do a project, the number of days for Party B to finish the project alone is less than that for Party A. if Party A works together for 2 days and Party B works for 3 days, how many days will it take for Party A to finish the project alone?
If a takes X days, then B takes X-2 days
The formula is the same as yours