7th grade math problems, to detail the process! Thank you

This face is 60 blocks, a difference of 15 blocks.

There are two cases before and after the hour hand.

Set to x points. then 40+5x 60-x= 15

or x=[(15)+40] (11 12) two roots.

Counting from 0:00 onwards.

The minute hand moves 360 60 = 6 degrees per minute.

The hour hand moves 360 (12 60) = degrees per minute.

The minute hand goes the first lap:

The first time it is vertical, the minute hand moves 90 degrees more than the hour hand.

The second time it is vertical, the minute hand moves 90 + 180 = 270 degrees more than the hour hand.

The minute hand goes on a second turn:

When it is vertical for the first time, the minute hand moves 360 + 90 = 450 degrees more than the hour hand.

The second time it is vertical, the minute hand moves 360 + 270 = 630 degrees more than the hour hand.

Then the minute hand goes the third turn, the fourth turn... All the way up to lap 12, the two verticals are:

and (360*10+900) 11

A total of 2 12 = 24 times.

The result here is how many minutes have passed since 0:00.

Then do the math yourself.

Between 8 o'clock and 9 o'clock, set 8 o'clock x minutes.

The needle is perpendicular to the minute hand.

Hour hand angle = 360 12 * (8 + x 60) = 240 + minute hand angle = 360 * x 60 = 6x

The hour hand is perpendicular to the minute hand, and there are two cases.

6x-（240+

Or. 240+

Solution x=60 (rounded).

or x = so, at about 8:27, the hour hand on the clock face is perpendicular to the minute hand.

Solution: The common idea of these questions is to make parallel lines of ab through p, and then use the nature of parallel lines to do the questions.

I'll pick question 1 and get a glimpse of the whole leopard.

1. AC two points are connected into a line segment to form a PAC triangle, the sum of the inner angles of the triangle is 180°, and the BAC and ACD are complementary angles, which are also 180°. So equation (1) holds.

2. Draw a parallel line with AB and CD through the P point. Establish.

3. The intersection point of the line segment is set to E, PEB= PCD, PEB+ AEP=180°, and the sum of the inner angles of the triangle is 180°, that is, PAB+ AEP+ APC=180°, PEB= PAB+ APC, which is established.

4, PA extension line to CD, the outer angle is equal to the sum of the non-adjacent angles, stands.

How to make a guide line is the key.

For Figure (1), the coupling AC can be seen as the triangle APC + angular BAC + angular DCA

For Figure (2), the extension of AP to Cd at E, then the angle PAB = angle AEC, and because the angle APC = angle DCP + angle AEC

For Figure (3), let AB cross CP and E, angle PEB = angle PCD, angle PEB = angle APE + angle PAB

For Figure (4) to extend the PA to E, then the angle PAB = angle PED, angle PED = angle APC + angle PCD

By the way, I will help you review the relationship between the triangle and the corners in the line of equality:

The isotope angles are equal, the inner angles are equal, and the side inner angles are complementary, and the outer angles of the triangle are equal to the two inner angles that are not adjacent to it, and this and!

Study hard!

The first figure: Connecting AC can be known: APC PAB PCD 360 degrees;

The second figure: connect the AC to know: APC PAB PCD;

3rd Figure: APC PAB PCD;

Fourth Figure: APC PCD PAB;

1. an=2n

2. a=4 b=2 c=8 d=5 e=7

142857x3=428571

3.(1) Profit from all rough machining = 4500x140 = 630,000

2) Finish as much as possible to make a profit = 7500x90 + 1000x50 = 725,000

3) Set the rough processing of the remaining vegetables after x days of finishing is just completed, then the rough processing is 15-x days.

By the inscription 6x+16(15-x)=140

So x=10=> 60t of vegetables processed in 10 days of fine processing, and 80t of vegetables processed in 5 days of rough processing

In this case, Profit = 7500x60 + 4500x80 = 910,000

So the third case is more profitable.

4.According to the minute hand is 360 60 = 6 ° per minute, and the hour hand is 30 60 = per minute

The first time was about 6:15, and it was set to be x minutes.

Then 180-6x+ gives x=140 11

The second time is about 6:50, set to be y minutes.

Then 360-6x+ y=580 11

So the person is out for a long time = y-x = 40 minutes.

5.The implicit condition is that the length of time the two iron rods are submerged in the water is the same.

So if the depth of the water is x, then the length of time that the two iron rods are submerged in the water is x

The length of the first iron rod out of the water is 1 3, and the length of the first iron rod is 1 3, and the length of the first iron rod is x (2 3)=3x 2

The length of the second iron rod above the water is 1 5, and the length of the second iron rod is 1 5, and the length of the second iron rod is (4 5)=5x 4

The sum of the lengths of the two iron rods is 55 3x 2+5x 4=55

x=20 cm.

Answer it well.

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I hate people lying to me the most, and of course I can't lie to myself. If you can't do the complicated, I'll teach you, and if the simple ones can't do it, then I won't teach you any of them, because there's no way to teach them. 17th at the latest?

What do you mean? I only teach people knowledge, will knowledge expire and deteriorate after the 17th?

This answer can solve your problem at its root. People are always moving forward in overcoming difficulties, and if you want to take shortcuts when laying the foundation, you will not progress. Contrary to your word, I believe in your future.

(1) A class holds a party, stipulating that each person must shake hands with other people once, and if n people in this class participate in this activity, a total of n 2 handshakes will be held.

2) A project A needs to be completed in a day alone, B needs to be completed in B days alone, and the amount of work completed by A and B in one day is 1 A+1 B

This kind of problem is a headache when you look at it.

(1) n-1

2) 1/A plus 1/b.

3) We have only just finished learning the mixed operation of rational numbers.

1.(m+n)<0 (m-n)<0 symbol: -2(m+n)-(m-n)=2m+2n-2m+2n)=4n.

times 4nomial, the highest coefficient is -3.

3.|2x+1|+(x-2a) = 0, |2x+1|>=0 ,(x-2a) >=0,|2x+1|=0 ，(x-2a)²=0，x= a=

4.(3k-2)x +(k-1)x+3=0 is a unary equation, then there is no x term, then k=2 3

Trouble, how to calculate the coefficient of 4 times 4 nomials, and the highest minor term?

The reply is not counted, it is watched.

The original planned time was 240 30 = 8 days.

The original plan was to sow the area per day = 2000 8 = 250 acres.

It was planned to sow 250 acres of wheat per day, but it was planned to sow for 8 days.