Elementary 1 math problems to be analyzed in detail .

2;If we know that 2x+y=5, then y=5-2x

Bring it into x+2y=4 and you get x+2(5-2x)=4

Solve the unary equation x=2 and substitute x=2 into 2x+y=5

y=1 can be calculated

So. x-y=2-1=1

3;Choose D....Because 1kg 16 eggs. So 1 million weighing 62,500kg is equal to 10 cars carrying 6t of cargo weighing 60tPlus the weight of the car itself. About yes.

4；120 degrees one dial is.

360°。8 a.m. The angle is 120°

5；The distance from the point to the line. The perpendicular line is the shortest (because I can't remember exactly, I forgot exactly what the theorem is called.) But that's what it means).

6；This can be tested. For example, 123....Completing the above steps results in the completion of step 600So. Student B guessed by subtracting 100 from the number obtained.

If you want a mathematical approach. You can set the original number to hundreds, and the number to xThe number of tens is yThe single digit is z....So the number is 100x+10y+z

From the above steps, [(5x+5) 2+y] 10+z can be obtained

Simplification to 100x+10y+z+100

The original number is 100x+1oy+z

So just subtract 100

7；Set up an electric mosquito coil for a dollar.

From the meaning of the title. Simplify it to greater than 1, so it is profitable.

The second question is to think about it for the time being.

I'll do it when I'm ready.

I worked on these questions all morning.

Just for you to say that you want to analyze it in detail.

x+2y=4

x=2 y=1

x-y=5.The straight-line distance between two points is the shortest.

The first question is (7+8)*2-6=24

The second question is to use a formula minus two machine 2x+y-x-2y=5-4 to get x-y=1, and the third question is the fourth answer, the reason is to estimate that an egg is 1 million grams, more than 60 tons, choose the fourth.

The fourth question is 120 degrees, which is exactly one-third of 360 degrees.

The fifth question seems to be the shortest straight line between two points, and I can't guarantee it.

Question 6 I won't be complicated.

Question 7 1+ This is to set the purchase price to 1 so lose This is the first question, the second question seems to be calculated like this, set into y, one is x yuan, and calculate xy=268, the result is a divisor, not necessarily right, only as a reference, the above questions are only for reference, not necessarily right, if wrong, bear with me.

2）x=1,y=3 x-y=-2

3) It should be B.

There's no time, I'll talk about it later.

2) The system of equations from the question: {2x+y=5

x+2y=4

Solution: {x=2

y=1 then x-y=1

3) 100000 16 = 62500 (kg) 62500 kg = ton.

Therefore, D4) The circumference of the clock disc is 360°, and it is divided into 12 large cells, then each large grid is 30°.

Hours 8 and 12 are 4 blocks apart, so: 4 30° = 120°5) What does "mean? Straight line? It should be the shortest vertical line segment to be used.

6) Hehe, if you bring in a three-digit number by yourself, you will find that the difference between the final number and your number is 100

This is where the "mystery" lies:

Use the hundredth digit 5, which is a multiple of 5. Add 5 to 2, and it becomes a multiple of 10, plus the number of 10 becomes a multiple of 10, and finally add the number of single digits, and the number in the ten place and the number in the single place are obvious. Let the number of hundreds be n, (5n+5) 2 10=100n+100, so the final number is one hundred more than the original number.

7) <1> (1+40%) 70%=98%, less than the purchase price, so it loses.

The second question is to go back and answer it again, you have to use your brain more, hehe.

It turns out that reading is so hard! Be a friend.

Solution: The paper is folded along a straight line through p, so that the straight line a on both sides coincides, and the crease c c a and c passes the point p

Then fold the paper again through the point p, so that the crease c on both sides coincide to obtain a new crease b b over the p point perpendicular to c

a c (two straight lines perpendicular to the same line parallel).

1.The 6th power is wrong because your answer is 3 significant digits.

2.1-4a+2a2 (the number of unknown numbers rises in the permutation, called the ascending power permutation).

3.The third question can only be solved in combination with the prerequisites. (Method: Absolute value of a non-negative number = itself, absolute value of a negative number = opposite number of itself).

The 6th power is right.

1-4a+2a²

The third question is that it cannot be simplified without preconditions

The b(a) line segments are all long, so they may not intersect; (c) If P is on the long line of the repercussions of AB, the straight line cannot be drawn parallel to AB, but can only coincide; (d) Assuming that the straight lines are horizontal, as long as Li Yu draws the CD in the direction perpendicular to AB, it will not intersect.

Personally, I think that all 4 answers can make corresponding diagrams, if you have learned the knowledge of space vectors or space geometry, you can think of it.

(-1 * 1/2) + (1/2 * 1/3) + (1/3 * 1/4) +1/2004*1/2005).

1.Rule: -1/n * (n+1) 1/1 = -1/n + (n+1) 12The original question can be obtained by applying the formula:

-n/1*(n+1)/1=-n/1 + (n+1)/1 n is a positive integer.

Make use of the above formula.

The formula is =-1 + 1/2 + (-1/2) + 1/3 + (-1/3) +1/2004 + (-1/2004) + 1/2005.

1 + 1 in 2005.

2005/2004

The law is -1 n*1 (n+1)=-1 n+1 (n+1)=(-n-1) n(n+1)+n n(n+1)=-1 n(n+1)=left.

Each multiplication term in the problem that is required to be calculated is replaced by the right side of the regularity, so that it can be canceled out before and after, and the result can be calculated quickly.

39 is an odd number, so when you pay 5 yuan, you need to take out an odd number, so that the rest of the money you need to pay is an even number, which is a multiple of 2 yuan to ask questions.