A few math problems will be written in a few ways

x-y=4 x+y=7

x-y)^2=16 (x+y)^2=49

x 2-2xy+y 2=16 x 2+2xy+y 2=49 plus to give 2*(x 2+y 2)=65

x^2+y^2=

2）a=12x

Can be transformed into 9x 2+4+12x=(3x+2) 23)x-1 x=2

x-1/x)^2=4

x^2-2+1/x^2=4

So x 2-1 x 2=6,4)a 2+b 2-2a+4b+5=0a-1) 2+(b+2) 2=0

The squares are all greater than 0, so it can only be (a-1) 2=0, (b+2) 2=0a=1, b=-2

a^b=15)x=a^2+b^2+20,y=4(2b-a)x-y=a^2+b^2+20-4(2b-a)a^2+4a+4+b^2-8b+16

a+2)^2+(b-4)^2>=0

So x is greater than or equal to y

6）a=7931,7931×7931-7930×7932=a^2-(a-1)*(a+1)=1

b=7935,c=7936

7934×7937+7935×7936=-(a-1)*(b+1)+ab=b-a+1=2

So the result is 3

7）a-b=4

a-b)^2=a^2-2ab+b^2

a+b)^2=a^2+2ab+b^2=(a-b)^2+4ab=16-4*(c^2+4)=-4c^2

a+b=2√-c

8) 18 right triangles.

5 obtuse triangles.

Acute triangles have [115-2*(18+5)] 3=69 3=139), and one case is ab+ad=21 cd+bc=12ab=ac=14, bc=5

In one case, ab+ad=12 cd+bc=21 cannot form a triangle.

2.+-12x or -4

4.The formula knows a=1, b=2, and the result is 1

5.Subtract and then formulate, x>=y

x*y-(x-1)*(y+1)=y-x+1=7936-7935+1=2, so we get 3

squared, a 2 + b 2-2ab = 16, ab + c 2 + 4 = 0, multiplied by 4, 4 ab + 4c 2 + 16 = 0

The two formulas are added, the formula is known, (a+b) 2+4c 2=0, known, a=-b, known, a=2, b=-2

8.There are right angles and obtuse angles are called right angles or obtuse triangles, so, right triangles 18, obtuse angles 5, the other angles in them are acute angles, therefore, 115-18 * 2-5 * 2 = 69, 369 3 = 23, there are acute angles 23

2) Plus or minus 12x

3）x^2-2+1/x^2=4

x^2+1/x^2=6

4) Original formula = (a-1) 2+(b+2) 2=0 a-1=0 and b+2=0 a=1, b=-2

5) x-y = (a+4) 2 + (b-4) 2 0 x y6) original formula = 7931 2 - (7931 + 1) (7931-1) - (7935-1) (7936 + 1) + 7935 7936

7) a=4+b, substituting b(4+b)+c 2+4=0, that is, (b+2) 2+c 2=0, that is, b=-2, a=2

8) Obtuse angle: 5, right angle: 18, acute angle: 23.

9）ab=ac=14，bc=5

Hope it helps.

1.It is known that x-y=4 squared on both sides (x-y) =4 x +y -2xy=16 so x +y =16+2xy

It is known that x+y=7 squared on both sides (x+y) =7 x +y +2xy=49 so x +y =49-2xy

So 16 + 2 x y = 49 - 2 x y 4 x y = 33 2 x y = 33 2 substituting x + y = 16 + 2xy

x²+y²=16+33/2=65/2

2.If 9x +4+a is a perfectly squared formula, 9x = (3x).

3x) +2 +a then a=2 2 3x=12x so a=12x

3.It is known that x-1 x=2, squared on both sides, (x-1 x) = 4

x²+(1/x)²-2×x×1/x=4

x +(1 x) -2 = 4 so x +(1 x) = x +1 x =6

4.It is known that a + b -2a + 4b + 5 = 0 divides the constant term 5 into 1 and 4

then where a -2a+1=(a-1) then the original formula is left b +4b+4=b +4b+2 =(b+2).

So the original formula a +b -2a + 4b + 5 = (a-1) +b + 2) = 0

So (a-1) =0 a=1 so (b+2) =0 b=-2

So the power b of a is both 1 and 2 and 1

y=4(2b-a)

If x-y is positive, then x y

x-y=(a+2) +b-4) 0 so x y

6.The easiest one should be the one downstairs.

a-b)²=a²-2ab+b²=16

a+b)²=a²+2ab+b²=(a-b)²+4ab=16-4×(c²+4)=-4c²

a+b=2√-c

8.No. cd+bc=12 ab=ac=14，bc=5

In both cases, only this is true, can form a triangle.

1.If the system of equations is solved synchronously, x= y=, then x2+y 2=

1. Time of encounter.

1 (1 20 + 1 30) = 12 hours.

Distance 1080 12*20=1800

Kilometers 2, time of encounter.

So when the distance between the two is exactly equal to half of the whole journey, the two of them just do 1 2, or 3 2 of the whole journey

So the time is.

5 7 hours, or 15 7 hours.

3. A efficiency.

B efficiency 1 2 5 = 1 10 common efficiency.

There is 1-1 3-1 5=7 15 left

It takes time. 7 15 (11 60) = 28 11 hours.

1080÷(1－20÷(20＋30))

The two cities are 1,800 kilometers apart.

After 5/3 of an hour, the distance between the two is exactly half of the whole time (1 1 3 1 5) (1 3 4 1 5 2) 7 15 11 60

There are still 28/11 hours to play.

1. I didn't understand the question, why was it 5km away from the end of the whole course when we met?

7 + 5 = 22 (twice the total number of pens) 22 2 = 11 brushes: 11-10 = 1 pencils: 11-7 = 4 pens: 11-5 = 6 A: 1 brush, 1 pencil, 6 pens.

3=66 yuan (total charter fee) 66*11=6 yuan (cost per ship) 6*7-22=20 yuan 6*4-22=2 yuan Answer: A: 20 yuan; B: $2.

1 = 14 games (1 player eliminated per game, 15-1 = 14 people need to be eliminated to determine the champion, that is, 14 games).

A: 14 games.

6. Solution: Let the third angle number be x degrees.

2*2x+x=180

5x=180

x=36 36*2=72 degrees.

Answer: It is an acute triangle; Isosceles triangle.

14 = 8 days.

Solution: If there are x days of rain, there will be (8-x) days of sunny.

12x+20(8-x)=112

160-8x=112

x=6A: There are 6 days.

8. Possibly: the total number of large and small people.

9. Solution: Let it be an X-side.

x-2)*180=1980

x-2=11

x=13A: Yes 13-sided.

Times. 1. Weigh 30 grams of salt.

2, the same as 13, the same as 1

4. Weigh 5 grams of salt.

5, same as 2; At this time, weigh out 100 grams of salt, 6, weigh 100 grams of salt.

7. Weigh 100 grams of salt.

The answer is not so sure).

(90+3)-2*90=99 points.

Answer: 99 points.

12. Solution: If there are x rabbits, then there are (100-x) chickens.

4x+2(100-x)=284

2x+200=284

2x=84x=32

A: There are 32 rabbits.

13. Solution: Set 8 cents stamp x, 4 cents stamp is (100-x) 68 yuan = 680 jiao.

8x+4(100-x)=680

4x+400=680

4x=280

x=70 100-70=30 sheets.

A: 70 stamps for 8 cents, 30 stamps for 4 cents.

14. Solution: If the answer is correct, the answer is wrong (20-x).

4x-4(20-x)=56

8x=56+80

x=17Answer: There are 17 answers.

15. Solution: If there are x motorcycles, then the car (24-x) vehicles.

3x+4(24-x)=86

96-x=86

x=10A: There are 10 cars.

1.It should be the midpoint. At this time, it is 5*2 10 less than A, so it takes 10 (15-10) 2 hours, and the whole journey is 2*(15+10) 50km

2.Pen + Pencil + Pen + Brush + Pencil + Brush = 10 + 7 + 5 = 22 Pen + Brush + Pencil = 11

Brush = 11 - pen + pencil = 1

Fountain pen = 7-1 = 6

Pencil = 5-1 = 4

The cost of team C should be the average cost of team A, B and C, that is, the cost of team A and team B is also 22 yuan, then the total cost of the three teams is 22 3 66 (yuan), the cost of each boat is 66 11 6 (yuan), and team A pays 7 6 42 (yuan) minus the cost of 22 yuan. He should get back 42-20 20 (yuan), and team B paid 4 6 24 (yuan) minus the 22 yuan he should pay, and he should get back 24-22 2 (yuan).

6. Let the third angle be x, then the sum of the other two corners is 2x, then 3x 180 x 60

Then the sum of the other two angles is 120 degrees, then this triangle may be a right triangle, an acute triangle or an obtuse triangle.

7. According to the meaning of the question, a total of 112 14 8 (days) are set, sunny days x, then rainy days are 8-x, according to the equation of the question column: 20x+12(8-x) 112: x 2

A: 2 days of sunny days and 6 days of rain.

8. If the rent is large x, the small is 11-x, and according to the title, 6x+4(11-x) 51 gets x

Well, they rent a big boat might be 4 and a small boat 7

9. According to the formula of 180 (n-2)=1980 for the inner angles of the polygon, n=13 is obtained, and this figure is a 13-sided shape.

10. A need to weigh at least 6 times with a balance, first weigh 3 times with 30 grams of code and then weigh twice with 5 grams of code to get 100 without salt, use this 100 grams of salt to weigh another 100 grams, and the rest is 100 grams.

11. I scored X points in the mathematics test, and I got it according to the question.

x+180＝93×3

Got: x 99

A: I scored 99 in mathematics.

12. Set x rabbits, then there are 100-x chickens, according to the title.

4x+2（100-x）＝284

Got: x 42

A: There are 42 rabbits.

13, set 4 cents stamps x, then 8 cents stamps 100-x, according to the title.

Got: x 30

A: 30 stamps for 4 cents, 70 stamps for 8 cents.

14. If you answer x correctly, then answer 20-x incorrectly, according to the question.

4x-4（20-x）＝56

Get x 17 Answer: She answered 17 correctly.

15. Set up a parking lot to park x motorcycles, according to the title.

3x+4（24-x）＝86

Get x 10

10 motorcycles.

7 + 5 = 22 (twice the total number of pens) 22 2 = 11 brushes: 11-10 = 1 pencils: 11-7 = 4 pens: 11-5 = 6 A: 1 brush, 1 pencil, 6 pens.

3=66 yuan (total charter fee) 66*11=6 yuan (cost per ship) 6*7-22=20 yuan 6*4-22=2 yuan Answer: A: 20 yuan; B: $2.

1 = 14 games (1 player eliminated per game, 15-1 = 14 people need to be eliminated to determine the champion, that is, 14 games).

A: 14 games.

6. Solution: Let the third angle number be x degrees.

2*2x+x=180

5x=180

x=36 36*2=72 degrees.

Answer: It is an acute triangle; Isosceles triangle.

14 = 8 days.

Solution: If there are x days of rain, there will be (8-x) days of sunny.

12x+20(8-x)=112

160-8x=112

x=6A: There are 6 days.

8. Possibly: the total number of large and small people.

9. Solution: Let it be an X-side.

x-2)*180=1980

x-2=11

x=13A: Yes 13-sided.