In the experiment of measuring resistance by voltammetry, it is unnecessary to () A. When connecting the circuit, first disconnect the switch B. the connection should start from the positive pole of the power supply, and the switch should be close to the positive pole of the power supply C. when it is impossible to estimate the measured resistance, the ammeter and voltmeter should choose a larger range D. when connecting the rheostat into the circuit, the slide should be placed at the position with the maximum resistance of the rheostat

A. When connecting the circuit, the switch should be disconnected in order to prevent short circuit, so a is not in line with the topic. B. It is unnecessary, as long as it can be connected normally and quickly, so B is in line with the topic. C. when it is impossible to estimate the measured voltage and current, the ammeter and voltmeter should choose a larger range

172 = 5 18 15= 140

18 × 5 △ 172, = 58 △ 172, = 45; 15 × 3 △ 140, = 35 △ 140, = 24; so the answer is: 45, 24

How many kilos is a pound and how to convert?
It's better to give the formula

1 lb = 0.4536 kg
1 kg = 2.20458554 LB

Several problems of quadratic equation of one variable in the third grade of junior high school
1. Given x ^ 2-xy-2y ^ 2 = 0 (Y ≠ 0), draw the graph of the point (x, y) satisfying the equation in the coordinate system.
2. Solve the following equation by formula method
（1）x^2-3ac+a^2=0
（2）kx^2-（2k+3）x+6=0（k≠0）

1. X ^ 2-xy-2y ^ 2 = (x + y) (x-2y) = 0, draw x + y = 0 and x-2y = 0 images
2. X ^ 2-3ax + A ^ 2 = 0, x = (9a * a-4a * a) / 2 = (5a) / 2
KX ^ 2 - (2k + 3) x + 6 = (kx-3) (X-2) = 0, x = 3 / K or 2

If a 40 Watt light bulb consumes one kilowatt hour, how many kilowatts of electricity can be saved if 25000000 40 Watt light bulbs are turned off in one hour
2. A person's height is about 1.60 meters when his arms are extended. How many hands does it take for her to reach a million meters?
3. We still have about two and a half years to go before the entrance examination. How many seconds are these two and a half years
4. It is known that one hundred yuan RMB is about 0.9 cm thick, one hundred yuan RMB is about 15.5 cm long and 7.7 cm wide, and how large a suitcase is needed to hold one million yuan RMB?

1. 25000000 * 40 = 1000000 kwh
2. 100 * 10000 / 1.6 = 625000 people
3. 2.5 * 365 * 24 * 3600 = 78840000 seconds
4. 10000 * 0.9 / 100 * 15.5 * 7.7 = 10741.5 cm3
A square box about 10 cm thick and 33.5 cm long

(a + 1) ^ 2 =? (A-1) ^ 2 =? A ^ 2 + B ^ 2 + C ^ 2-2a + 4b-6c + 14 = 0?

a^2+b^2+c^2-2a+4b-6c+14=0==>
(A-1) ^ 2 + (B + 2) ^ 2 + (C-3) ^ 2 = 0 = = > must be A-1 = 0, B + 2 = 0, C-3 = 0
A=1,B=-2,C=3
So a + B + C = 1-2 + 3 = 2

Whether it is a series circuit or a parallel circuit, under the same conditions, is the total electric work the same? (for example, first connect two resistors of 3 ohm in series, and then change to parallel) why?
Let the total voltage and the resistance be constant.

The total resistance in series is different from that in parallel. The resistance in series is larger than that in parallel. Therefore, under the same voltage, the total current is different. Therefore, the total electric power is also different. That is, the resistance in parallel is larger than that in series

Known a

∵(3m+2)a ≥ (3m+2)b
∴(3m+2)a-(3m+2)b ≥ 0
Therefore:
(3m+2)(a-b) ≥ 0
Again

Electric power = electrician * time, which electrician refers to voltage or what

The work done by electricity,

As for the stiffness coefficient K of spring, the following statement is correct
A. For the same spring, the stiffness coefficient under compression is greater than that under tension
B. The longer the spring is pulled, the greater the stiffness coefficient is
C. The stiffness coefficient of spring increases with the increase of tension
D. Each spring has its own inherent stiffness coefficient

If D is in the range of stiffness, the stiffness coefficient remains unchanged

______ 172 = 5 18 15=______ 140

How many kilos is a pound and how to convert? It's better to give the formula