Ask geometric math questions 1. There are innumerable straight lines passing through a point; there is one and only one straight line passing through two points, and the straight line passing through three points does not exist. Question: if point C is not on the line AB passing through two points a and B, then () the straight line passing through points a, B and C

A. B. There are only three straight lines that do not pass through a point
Because point C is not on the straight line AB passing through a and B, then C and ab can only form a triangle and cannot form a straight line~

The water level of a reservoir has exceeded the warning line, and the upstream river still flows into the reservoir at a cubic meter per second. In order to prevent flood, it is necessary to open sluice gates. Assuming that each gate discharges water at a flow rate of (a2-3) cubic meters per second, it is estimated that if one sluice gate is opened, the water level can be lowered to the warning line within 15 hours; if two sluice gates are opened, the water level can be lowered to the warning line within 5 hours Value

1 hour = 3600 seconds,
When the water is discharged: the inflow water is 15 × 3600a cubic meters in 15 hours, while the discharged water is 15 × 3600 (a2-3)
The inflow water plus the excess water is equal to the discharged water
15×3600a+x=15×3600（a2-3）①
When two discharges: 5 hours, the inflow water is 5 × 3600a m3, and the discharged water is 2 × 5 × 3600 (a2-3)
Similarly, the inflow water plus the excess water equals to the discharged water
5×3600a+x=2×5×3600（a2-3）②
At this time, we can get the following results: 1
5×3600a+x-（15×3600a+x）=2×5×3600（a2-3）-[15×3600（a2-3）]
That is, a2-2a-3 = 0
The solution is A1 = - 1 (omit), A2 = 3
A: the value of a is 3

Given the function f (x) = √ x + 1, then f (3)=____ I don't know whether it is 2 or plus or minus 2. Under the explanation, I think I have plus or minus 2 because it is very simple but easy to make mistakes

F (3) = √ 3 + 1 = √ 4 = 2, because √ 4 means arithmetic square root, there are no two square roots, only one positive, so the answer is 2, there is no negative answer

Ask junior high school mathematics question how to do? How much is [2-2 squared-2 cubic-2 cubic-2-quartic-2-quintic-2-6th-2-octave-2-9th-2-10th] known [2-10-2-2-9 = 2-9 times (2-1) = 2-9th power] please write down the detailed process

2-2 squared-2 cube-2 cubic-2-quartic-2-quintic-2-6th-2-octave-2-9th + 2-10th
=The tenth square of 2-2, the ninth cube, the eighth power of 2, the seventh power of 2, the sixth power of 2, the fifth power of 2, the fourth power of 2, the third power of 2, the square of 2, and 2
=The ninth cube of 2-The eighth power of 2-The seventh power of 2-2-the sixth power of 2-2-the fourth power of 2-2-the cubic-2 of 2 + 2
=The eighth power of 2 - the seventh power of 2 - the sixth power of 2 - the fifth power of 2 - the fourth power of 2 - the cubic - 2 of 2 + 2
=The seventh power of 2 - the sixth power of 2 - the fifth power of 2 - the fourth power of 2 - the cubic - 2 - the square of - 2 + 2
=The sixth power of 2 - the fifth power of 2 - the fourth power of 2 - the cubic - 2 - the square of - 2 + 2
=The fifth power of 2 - the fourth power of 2 - the cubic power of 2 - the square of - 2 + 2
=The fourth power of 2 - the cubic of 2 - the square of - 2 + 2
=Cubic of 2 - cube of 2 - square of 2 + 2
=-Square of 2 + 2
=-2
I don't know if you've subtracted an extra cubic of two, if so
=The square of - 2
=Cube of 2 - square of 2 + 2
=Square of 2 + 2
Six

(50+5x) (120-6x) =-30 (X-5) square +6750 The answer is to ask how to get the answer!

Left = - 30x ^ 2 + 300X + 6000
=-30(x^2-10x+25-25)+6000
-30(x-5)^2+750+6000

The electromotive force of the power supply is 1.5 V, the internal resistance is 0.2 Ω, and the resistance of the external circuit is 1.3 Ω. The current in the circuit and the voltage at both ends of the external circuit resistance are calculated

I=U/(R+r）=1.5/(1.3+0.2)=1A
Uexternal = IR = 1 * 1.3 Ω = 1.3V

Ask physics questions There is a thermometer scale is not accurate, so the indication in the ice water mixture is 5 ℃. The boiling water temperature under standard atmospheric pressure is 95 ℃. The temperature measured by this thermometer is 32 ℃. What is the actual temperature?

Therefore, in the ice water mixture, the indication is 5 ℃, and the boiling water temperature at standard atmospheric pressure is 95 ℃
It can be seen that the actual temperature is 0-100 degrees, but there are only 90 scales, so from 5 to 95 degrees, each represents 100 / 90 degrees. The actual temperature at 32 degrees Celsius is (32-5) * 100 / 90 = 30,

As shown in the picture, put both hands into hot and cold water at the same time. After a period of time, take out both hands and put them into warm water at the same time (choose "the same" or "different") .

The first temperature of the two hands is different, and the conclusion drawn by putting them into the same warm water is different. This is because the criteria of the two judgments are different. This fact shows that it is not reliable to judge the temperature of an object by feeling
So the answer is: not the same; it is not reliable to judge the temperature of an object by feeling

If someone can lift an object with a mass of 60 kg on the ground, and can lift an object with a maximum mass of 80 kg in an accelerated descending elevator, the acceleration of the elevator is_ If the elevator is accelerated at this acceleration, the maximum mass that the person can lift in the elevator is 0 (g = 10m / S ^ 2) It's better to write down the process

When a person can lift a 60kg object on the ground, the maximum upward force is 600N. When the elevator is accelerating and descending, the elevator and all the objects in the elevator have downward acceleration and are in weightlessness

If an object is placed 20 cm away from the lens and can be magnified three times, the focal length of the lens may be - cm or - cm

More than 20 cm or less than 10 cm