A few math problems, please help the immortals, remember the writing process!

One. 1.Analysis: Lending 11 15 and leaving 4 15, and then buying 240 copies becomes the original 1 3, so 240 copies account for the original 1 15, process: 240 (1 3-4 15) = 3600 (book).

2.Analysis: Team A worked 1 30, Team B worked 1 20, and Team B worked alone for 10 days to complete 1 2

Process: (1 2) 15 = 1 30 (1 5) 4 = 1 20 (1 20) 10 = 1 2

1-1 2) (1 30 + 1 20) = 6 (days).

3.Set x cars, according to the topic, 3x+15=4x-35, the solution is x=50, so 50 cars, 3 50 + 15 = 165.

Two. Original = (56+1)(56-1) 56+(28 -55) 28

Hope it helps.

1.After buying 240 books, the books in the library were 1/3 of the original, that is, 5/15; Before the 240 books were bought, there were 4/15 of the books left in the library, that is, 240 books were 1/15 of the total (5/15-4/15), and there were 3,600 books.

2.B completes 20 1 of the total project in one day, and A completes 30 1 in one day; Team B working alone for 10 days is 2 1, two teams working together for one day is 12 1, and there are 2 1s left, which will take 6 days.

3. 1 times of the passenger car is 15 + 35 = 50 cars.

There are 165 buses.

Two. 56²-1/56+28²-55/28

I said: Use your own brain, have enough food and clothing.

Solution: Derive a wide search according to the principle of parallelism.

The angle of reflection of the included and the number of lands through the plane mirror are respectively , and the number of angles of incidence is always equal to the angle of reflection.

Plane carefully complete the reflection angle of the mirror

In opp'The sum of the inner angles is 180°

From the title, it can be seen that this Qiao's commodity ** to buy acacia oak this time.

90x（1—19%）=

Therefore, the percentage of the price reduction is x

Get. 90x（1—x）^2=

1—x）^2=

1 - lead width next x) 2=

1—x）=x=1—

x = so the percentage of the price reduction is 10%.

Let the original speed of the car be xkm h, then the speed after the failure is (x-9) km h

108 x+24 60=108 (x-9) gives x1=54 and x2=-45

The test shows that x=54 is the solution of the original equation.

If you solve it with an equation, you will definitely be able to solve it!

d is the midpoint of ab.

So ad=1 2ab=1 2ac bac=90°, so adc=60°

AF Vertical CD

So daf=30°

Because be ac

abe=∠bac=90°

be=1/2ab=db

DBE is an isosceles right triangle.

acb=∠abc=45°

BC is perpendicular and bisected

, the manuscript is x

Xiao Ming can play x 5 in an hour

2 3x divided by x 5 = 3

Therefore, Xiao Ming still needs three hours to finish.