Help me solve a math problem, analyze and do the process.

Let's say your call time is x, then.

With 139, the monthly call rate is y1=50+

With 136 monthly phone bills for y2=

When Y1 = Y2, X = 250, that is, the talk time is 250 minutes, when Y1 > Y2, X<250, when Y1250, when you use 136 mobile phones, the monthly call fee is more than 150, that is, the monthly call time is more than 250 minutes, that is, it is greater than 250, which is the third case, that is, it is very cost-effective to change mobile phones.

Pay. With 136 mobile phones, the monthly bill is more than 150, and the talk time is at least 150 minutes per month).

If you use a global mobile phone, the call is 250 minutes, and the monthly billing is RMB).

If you only talk for 250 minutes, the phone bill of the two mobile phones is the same, but for every additional minute of call per month, 139 yuan will only increase, and 136 mobile phones will increase yuan, so it is more cost-effective to change mobile phones for more than 250 minutes.

1. 200 minutes of local calls, global pass fee: RMB.

200 minutes, Shenzhou trip fee: yuan.

300 points for local calls, global pass fee: yuan.

300 points for local calls, Shenzhou trip fee: yuan.

2. There will be the same charge for the two billing methods: when the local call is 250 minutes.

Global Pass Fees:

Shenzhou trip fee:

3. If he calls less than 250 minutes per month, it is recommended that he choose the Shenzhou Travel Card, and if it is more than 250 minutes, he should choose the Global Card.

Pay. 150 divided by 150 to indicate that the ** played is greater than 250;

If 251** are called, the global mobile phone will cost yuan (plus monthly fee) and the mobile phone will need yuan;

Therefore, it is cost-effective to use mobile phones around the world.

Scale 1:

Two numbers = x, the sum remains unchanged or 18

x+x=180/37

Two numbers = x, =180 37 , 486 37

Solution: (1) The cost of using an energy-saving lamp is Y (1) yuan, and the cost of using an incandescent lamp is Y (2) yuan

y（1）＝49＋ ·

0≤x≤2800）

y（2）＝18＋ ·

0≤x≤2800）

2) (1) y(1) y(2) i.e. solution: x 2000 i.e. when the lighting time is 2000h, the cost of using both lamps is the same.

2) When x 1000, y(1).

Yuan) y(2).

38 (yuan).

When x 3000, y(1).

Yuan) y(2).

78 (yuan).

Obviously when 0 x 2000, y(1) y(2) when 2000 x 2800, y(1) y(2) answer (omitted).

3) If the time for using energy-saving lamps is xh, the time for using incandescent lamps is (3000 x)h, and the total cost is (

0≤x≤2800）

Obviously, when x 2800, W is minimal

Yuan) A (omitted).

1) Energy-saving lamp cost = 49 + multiplied by x.

Incandescent lamp life = 18 + multiplied by x.

2) Set the lighting time x.

49+ multiplied by x multiplied by x multiplied by.

Solve x=2000

The last two questions can be launched according to the second question.

First, the cost of energy-saving lamps: 49+ incandescent lamp costs: 18 + two, (1) 49 +

x=1000 When 1000 hours of illumination, the usage cost is the same.

2) When the illumination is equal to 1000 hours, the usage cost is the same.

When the illumination is greater than 1000 hours, energy-saving lamps are used.

When the illumination is less than 1000 hours, an incandescent lamp is used.

Third, because when the lighting is less than 1000 hours, it is more economical to use incandescent lamps, and when the lighting is more than 1000 hours, it is more economical to use energy-saving lamps.

So: 49 + = yuan).

The first time A is poured to B: There is 480g in cup A, concentration = 1;There are 1120g in cup B, and the concentration = 480 1120 = 3 7

B poured to A: There is 1040g in cup A, concentration = (560 * 3 7 + 480) 1040 = 9 13;There are 560g in cup B with a concentration = 3 7

The second time A pours to B: 520g in cup A, concentration = 9 13;There is 1080g in cup B, and the concentration = (520*9 13+560*3 7) 1080=5 9

B poured to A: There is 1060g in cup A, concentration = (520 * 9 13 + 540 * 5 9) 1060 = 33 53;There are 540g in cup B with a concentration = 5 9

The third time A pours to B: There are 530g in cup A, and the concentration is 33 53;There is 1070g in cup B, and the concentration = (540*5 9+530*33 53) 1070=63 107

B poured to A: There is 1065g in cup A, concentration = (535 * 63 107 + 530 * 33 53) 1065 =; There are 535g in cup B with a concentration = 63 107

So, the solution in cup A has 1065 grams, and the concentration is:

It made my hands sore!

If there are 20 boys and girls, then there are 20 more boys than girls, but now there are actually 30 more boys than girls, indicating that there are more boys than girls.

When there are 21 boys and 19 girls, except for the same number of men and women (19 people), the two boys plant 3*2=6 trees, and the boys plant 19+6=25 more trees than the girls.

In the same way, when there are 22 boys and 18 girls, except for the same number of men and women (18 people), the extra four boys plant 3*4=12 trees, and the boys plant 18+12=30 more trees than the girls.

If there are x boys, there will be 40-x girls, 3x trees planted by boys, and 2 (40-x) trees planted by girls.

Male students planted 30 more trees than female students.

3x-2（40-x）=30

Solve the equation 3x-80+2x=30

5x=110

x=22 girls, 40-x=40-22=18.

Set up boy x person, girl y person, get:

x+y=40……①

3x-2y=30……②

Then there is , get: x=22, y=18, that is, 22 boys, 18 girls.

There are x boys and y girls.

Equations are set by known conditions.

x+y=40

3x-2y=30

2. Find the size of the carton that needs the area of the washing machine, that is, find the surface area of the washing machine Cuboid surface area formula: (length, width, width, height, length and height) 2. Substitute the known conditions into (54 50 50 95 54 95) 2 25160cm

5. This question is the same as the previous question.

Substituting the formula But it should be noted that the ground and doors and windows do not count.

So it is: (width height length height) 2 length width

Substituting the known conditions into the above equation.

The title of that kind of show of affection is either 520 or 1314520. Alas, I have been single for a long time and have developed indecently at my own perk.

According to the question functions, f(x) and g(x) can be reduced to f(x) (and g(x) 520+x +lg(2021-x)-lg(2021+x) 2, respectively

When x -520 and x 520 f(x) have a minimum value l ( and a maximum value o (, when x -2020 and x 2020 are g (x) have a maximum v (520-2020 -lg4021 2 and a minimum value p (520 + 2020 + lg4021 2, respectively

So L+O+P+V

Cross m to make a parallel line of ab, and cross ad and f

f is the midpoint of AD.

Angular CDM = Angular ADM = Angular DMF

Triangle dam isosceles.

af = fmfam angle = angle fma = angle mAb

AM is divided.

[Analysis].

Inverse matrix definition: If the nth-order matrix a and b satisfy ab=ba=e, then a is said to be reversible, and the inverse matrix of a is b.

Answer] a -a +3a = 0, a (e-a) + 3 (e-a) = 3e, a + 3) (e-a) = 3e

e-a satisfies the definition of reversible, and its inverse matrix is (a +3) 3 [commentary].

Theorem: If a is an nth order matrix with ab=e, then there must be ba=e.

So when we have ab=e, we can directly use the inverse matrix definition. There is no need to determine ba=e.

For such abstract matrices, you can consider using definitions to solve them.

If it is a concrete matrix, it can be solved by elementary transformations.

Linear algebra includes determinants, matrices, systems of linear equations, vector spaces and linear transformations, eigenvalues and eigenvectors, diagonalization of matrices, quadratic forms, and application problems.

(1) From x2-2x-8=0, x1=-2, x2=4, therefore, the coordinates of the two intersections of the parabola and the x-axis are (-2,0), (4,0) (2) y=x2-2x-8=(x-1)2-9, and the coordinates of point c are (1,-9).

There is ab=|-2-4|=6，s△abc=

Hello! Solution: Let A and B produce x and y parts per hour, according to the topic

8x+6y=312

5y=2x solution gives x=30

y=12, so the number of parts produced by A and B is.

8x=8*30=240 (pcs).

6y=6*12=72 (pcs).

A: A and B produce 240 and 72 parts respectively.

B's 5 hours of work is equal to A's 2 hours of work, and B's 1 hour of work is equal to A's 2 5 = hours).

Now, B has produced 6 hours, which is equivalent to A has produced: *6= (hours), A has produced 312 (8+) in one hour

A 8 hours produced: 30 * 8 = 240 (pcs) B 6 hours produced: 312 -240 = 72 (pcs).