Find the extremum of the function u = x-2y + 2Z under the additional conditions X & # 178; + Y & # 178; + Z & # 178; = 1

Find the extremum of the function u = x-2y + 2Z under the additional conditions X & # 178; + Y & # 178; + Z & # 178; = 1

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2x+y+2z=4 3x-2y+z=11 x+y+2z=-2

2x+y+2z=4①
3x-2y+z=11②
x+y+2z=-2③
①-③：x=6
②×2：6x-4y+2z=22④
④-①：4x-5y=18⑤
Substitute x = 6 into 5
y=1.2
Substitute x = 6, y = 1.2 into 3
z=-4.6
So: x = 6, y = 1.2, z = - 4.6

If the isosceles trapezoid ABCD is circumscribed to a circle and the median line Mn is 12 cm, what is the circumference of the trapezoid ABCD

The median line Mn is 12 cm long
It means that the sum of the top and bottom is 24cm
Also isosceles trapezoid ABCD circumscribed in circle
So the sum of the two waists is the sum of the upper and lower bottoms, which is 24 cm
Therefore, the circumference of trapezoidal ABCD is 48 cm

If 2n + 1 power of 3 + 2n power of 3 = 324, try to find the value of n

3^（2n+1）+3^2n=3243*3^2n+3^2n=3244*3^2n=3243^2n=812n=4n=2.

Sum: 1 + 11 + 111 + 1111 + 111... 1 (111... 1, n ones)

The original formula is: 1 * n + 10 * (n-1) + 100 * (n-2) +... + 1 * 10 ^ (n-1)
Just simplify

Solving equations 2x + y = 1 4x-2y + Z = 3 6x + y-3z = 0

2x+y=1 .(1)
4x-2y+z=3 .(2)
6x+y-3z=0.(3)
(2) * 3 + (3) gain
18x-5y=9.(4)
(1) * 5 + (4) gain
28x=14
x=0.5
Substitute (1) to get
1+y=1
y=0
Substitute (3) to get
3+0-3z=0
z=1
Solution
x=0.5
y=0
z=1

Voltage and current problems in parallel circuit
This circuit is a parallel circuit of two small bulbs in parallel, once again no other electrical appliances
The total voltage of parallel circuit is equal to the sum of branch voltages. How to understand this sentence? I just said that this circuit has two branches. The total voltage is equal to the sum of the voltages of the two branches. What about the current
Come again a person who doesn't look at the question to supplement the answer. Is it easy to make money without thinking?

Your topic is absolutely wrong
Voltage relation of parallel circuit: the voltage at both ends of each branch is equal
Current relation: the current of trunk is equal to the current of each branch
Voltage relationship of series circuit: the total voltage is equal to the sum of the voltages at both ends of each electrical appliance
Current relation: the current is equal

Divide the fraction 9m ^ 2-N ^ 2 / 3M ^ 2 + Mn

The formula should be (9m ^ 2-N ^ 2) / (3m ^ 2 + Mn);
The molecule can be reduced to (3m + n) (3m-n) according to the square difference formula
M (3m + n) can be extracted from denominator;
The original formula = (3m-n) / M = 3-N / M can be obtained by dividing the numerator and denominator;
That's what we want

The name plate of Xiaoming's electric kettle is shown in the figure. Under a standard atmospheric pressure, when the kettle works normally, it can boil 2kg water at 10 ℃ in 10min. The specific heat capacity of water is 4.2 × 103J / (kg & # 8226; ℃)
Dashan brand electric kettle
Model: nh-520
Power supply: 220 V, 50 Hz
Rated power: 1500W
Q: 1. Calculate the heat absorbed by water
2. Calculate the consumed electric energy

1. Q suction = cm △ t = 2kg × 90 ℃× 4.2 × 103J / (kg ᦇ 8226; ℃)
=7.56×105J
2.W=PT=10MIN×60S×1500W=9×105J

Simplify (2a-a * a) (a * a + 4A + 3) / (a * a * a + A * a) (a * a + a-6), and find the value of this fraction when 4A + 3 / a = 0

The original formula = - A (A-2) (a + 3) (a + 1) / [A & sup2; (a + 1) (a + 3) (A-2)]
=-1/a
(4a+3)/a=0
4a+3=0
a=-3/4
Original formula = 4 / 3