Big brothers and sisters do me a favor in junior high school math

1.7-2xy-3x 2y+5x 3y 2z-9x 4y 3z 2, which is arranged by the power of the letter (x).

2. -3a+3a=-3(a-a), 2a-2a=2(a-a),5a-5a=-5(a+a), 4a+4a=4（a+a）。

xy=3, then 3xy-7x+7y=(-26).

4.Knowing ab=3,a+b=4, find the value of 3ab-[2a-(2ab-2b)+3].

3ab-[2a-(2ab-2b)+3]

3*3-[2(a+b-ab)+3]

5. x-2(1-2x+x^2）+3（-2+3x-x^2）

x-2(1-2x+x^2）+3（-2+3x-x^2）

x-2+4x-2x^2-6+9x-3x^2

5x^2+14x-8

6.If the value of (x 2+ax-2y+7)-(bx 2-2x+9y-1) is irrelevant to the value of the letter x, find the value of a and b.

x^2+ax-2y+7)-(bx^2-2x+9y-1)

x^2+ax-2y+7-bx^2+2x-9y+1

1-b)x^2+(a+2)x-11y+8

It has nothing to do with the value of the letter x.

Make 1-b=0, ==>b=1

a+2=0,==>a=-2

1.7-2xy-3x to the power of y + 5x to the power of y's power z-9x to the fourth power of y's power z, is arranged by the letter (x) as a power (liter).

2. -3a+3a=-3( a-a ),2a-2a=2( a-a ),5a-5a=-5( a+a ),4a+4a=4（a+a ）。

xy=3, then 3xy-7x+7y=(-26).

4.Knowing ab=3,a+b=4, find the value of 3ab-[2a-(2ab-2b)+3].

3ab-[2a-(2ab-2b)+3]

3ab-[2(a+b)-2ab+3]

1.It is arranged by the power of the letter (x) as a liter.

3ab-(2a-2ab+2b+3)

3ab-2a+2ab-2b-3

5ab-2a-2b-3

5ab-2（a+b）-3

X and Y are expressed with m, x=1-my=2m-23, and then brought in x+y=7 to give m=203

Treat a as a known number, denote x, y as a, solve the equation, x=2a-12, y=8-a, back generation, a=26

Kilometer-hour = 1-meter-second.

Unary equations laugh then:

If the speed of the train is x meters and seconds, then the length of the train is (x+1)*15 meters.

x+1)*15=(x-1)*17

x = 16 m sec.

The length of the car is (x+1)*15 = 255 meters.

Binary Linear Equation:

Let the train be x meters long, and the speed of the train will be y meters and seconds.

y+1)*15=x

y-1)*17=x

y = 16 m sec x = 255 m.

The speed of the train is x kilometers per hour.

x+x=length of the train = (km.)

Take the length of the train as the same amount of transport.

Let the waist length of the triangle ABC be X and the bottom length be Y

It is discussed in two situations.

1) x+(x2)=12, (x2)+y=15, x=8, y=11

2) x+(x 2)=15, (x 2)+y=12 to get x=10, y=7

So the waist length of the triangle ABC is 8 and the bottom length is 11, or the waist length is 10 and the base length is 7

There are two cases, 1) if ab+ad=12, bc+cd=15

And, ad=cd,ab=ac,ab=2ad,ab+ad=12,3ad=12,ad=4,ab=2ad=8=ac,bc=15-4=11

2) If ab+ad=15, bc+cd=12

3ad=15,ad=5,ab=10=ac.

bc=27-20=7.

10, 10, 7 or 8, 8, 11

Let ab=ac=x, bc=y, then there is the equation:

2x+y=12+15；

or 2x+y=12+15;

Solve the first set of equations: x=8, y=11;

Solve the second set of equations: x=10, y=7;

Let the time of the encounter be x minutes.

x+4=3x

The distance of x=2p is 2 5=10

Divide Kafka to garbage Araki.

Forehead ......Can I say no?

50+36) 2=43 50-43=7 36-43=-7 So shift A transfers 7 people to shift B.