A few math problems in the seventh grade are answered by experts

1) get triangles; The triangle has stability.

2) 135 degrees.

3) Triangle congruence can be used.

It plays a stabilizing role, using the stability of the triangle.

In the RT triangle ABC, the angle C = 90 degrees, then the sum of the angle CAB and the angle ABC is 90°, because these two angles have an angular bisector so 1 2 (angle CAB and angle ABC) = 45°, that is, the angle OB + angle ABO = 45°, so in the triangle AOB the angle AOB = 135°

Fixed triangles have stability.

The first plot is the overlap of the midline and the angular bisector.

2 are isosceles triangles in three-in-one.

3 are overlapping high and angular bisectors.

I can see it.

Oh, the answer is not good, please don't be surprised.

Question 1:

Set the sales price to x, and sell y pairs, then there is.

200 x 8 (y 200) x 10 9990, i.e. (y-40)*x=99900

There is x is a two-digit prime number, and x=37,y=2740 is found in the second question:

The speed that the computer accepts is kilobytes, and the speed of transmission is kilobytes, so the combined velocity is 1 kilobyte.

1) Send first: After 4 turns, in addition to the newly accepted data, an additional 40 kilobytes are sent, and the original data in the computer is still 58-40=18 (kilobytes) 18 seconds).

So: a total of 20 * 4 + 90 19 = 84 and 14 19 (seconds) (2), first accept: after 5 turns, an extra 50 kilobytes are sent.

There is still 58-50 = 8 (kilobytes) (8 + seconds) of the original data in the computer

So:A total of 20 * 5 + 180 19 = 109 and 9 19 (seconds) false fractions should be okay.,If you can't, make your own decimals.,That's it.,I hope it can help you.

Hello, question 2 can't read clearly, is it a number to the power of 0? That's 1, and the power of zero of any number is 1, except for 0.

Question 1: A to the (2n) power.

x to the power of (2m+3).

1.According to the title, 2a+b+2=7

3a+3b-9=3

The original system of equations can be reduced to.

2a+b=5①

a+b=4②

Get. 3a=1

a=1 3 substitute a=1 3.

1/3+b=4

b=13/3

So one-third 6=1 3*(1 3)+13 3*6+1 3*6=28 and 1 9=253 9

2.The speed of the person is xkm min, and the speed of the car is ykm min, according to the question.

6（y-x）=2（x+y）

6y-6x=2x+2y

4y=8xy=2x

The distance between each two vehicles is 2*(x+2x)=6x

t=6x/（2x）=3

A: There is a car every 3 minutes.

Question 1: Because x y = ax + by+ xy, substituting 2 1 = 7, where a and b are constants, then 7 = 2a + b + 2 * 1

In the same way, substituting (-3) 3=3 gives 3=(-3)a+3b+(-3)*3

Solution 2a+b+2*1=7

3）a+3b+（-3）*3=3

A system of equations, find the values of a and b a=1 3 b=13 3 substituting a=1 3 b=13 3 into x y=ax+by+xy to get x y=1 3x+13 3y+xy, and then substituting one-third 6 into x y=1 3x+13 3y+xy to get 1 3*1 3+13 3*6+1 3*6=253 9

The specific values will be calculated.

1. Solution: Bring x=2 y=1 into ax+by+xy=7 to get:

2a+b+2=7

2a+b=5 ①

Substituting x=-3 y=3 into ax+by+xy=7 to obtain.

3a+3b+(-9)=3

3a+3b=12, synthesis, to obtain the system of equations: 2a+b=53a+3b=12

3, get: 6a+3b=15, get: 9a=3

a=1 3 brings a equal to 1 3 into , gets.

b=13/3

So the original ax+by+xy=1 3x+13 3y+xy substitutes, x=1 3 y=6, and we get 1 3 1 3 +13 3 6+1 3 6=253 9

2: Solution:

1.Minimum zero, maximum 1.

2.A minimum of 0 and a maximum of 3.

3.Minimum 0, maximum 6.

4. Memorize the formula:

5. There should be definitions and explanations in the math book:

Static Definition of Angle: A two-part graph of a ray group with a common endpoint is called an angle. This common endpoint is called the vertex of the angle, and these two rays are called the two edges of the angle.

Dynamic definition of an angle: The shape formed by a ray rotating from one position to another around its endpoint is called an angle. The end point of the rotated ray is called the vertex of the angle, the ray at the beginning position is called the beginning edge of the angle, and the ray at the end position is called the end edge of the angle.

Symbol of the Horn:Symbol of the Horn:

Types of horns. The size of the corner has nothing to do with the length of the edge; The size of the angle is determined by how far apart the two sides of the horn are, the larger the opening, the larger the angle, and conversely, the smaller the opening, the smaller the angle. Angles can be divided into 10 types: acute angles, right angles, obtuse angles, flat angles, circumferential angles, negative angles, positive angles, superior angles, inferior angles, and 0 angles.

Acute angle: Angles greater than 0° and less than 90° are called acute angles.

Right angle: An angle equal to 90° is called a right angle.

Obtuse angle: Angles greater than 90° and less than 180° are called obtuse angles.

Flat angle: An angle equal to 180° is called a flat angle.

Optimal angle: greater than 180° and less than 360° is called optimal angle.

Inferior angle: greater than 0° and less than 180° is called inferior angle, acute angle, right angle, and obtuse angle are all inferior angles.

Circumferential angle: An angle equal to 360° is called a circumferential angle.

Negative angle: An angle that rotates in a clockwise direction is called a negative angle.

Positive Angle: The angle that rotates counterclockwise is a positive angle.

0 angle: An angle equal to zero degrees.

Co-angle and complementary angle: If the sum of the two angles is 90°, the two angles are co-angles with each other, and if the sum of the two angles is 180°, the two angles are complementary angles to each other. The co-angles of equal angles are equal, and the complementary angles of equal angles are equal.

Opposite vertex angles: After two straight lines intersect, there is only one common vertex and the two sides of the two corners are opposite to each other, so the two angles are called opposite vertex angles. Two straight lines intersect to form two pairs of opposite vertex angles. The two angles that are opposite each other are equal.

There are also many angles, such as the wrong angle, the same angle, and the same side inside angle!

That's enough, right!?

1. A minimum of 0 and a maximum of an infinite number.

2. A minimum of 0 and a maximum of an infinite number.

3. Up to an infinite number of them.

4. Up to an infinite number of them.

5. An angle is composed of two rays with a common endpoint, and these two rays are the two sides of the angle.

4.There are several intersection points when n straight lines intersect in pairs, and there are up to n*(n-1) 2 intersection points.

5.The graph consisting of two rays with a common point is called an angle, and these two rays are called the two sides of the angle.

1.The minimum number of intersections is 0. The maximum number of intersections is 1.

2.Draw three lines on a plane with at least 0 intersections. The maximum number of intersections is 3.

3.Draw four straight lines on a plane, and the maximum number of intersections is 6.

4.Draw n straight lines on a plane, and the number of intersections should be at most n(n-1) 2 5Definition of an angle: An angle consists of two rays (with common endpoints), which are the two sides of the angle.

5x4 to the power + 3x2 to the power y-10-3x2 to the power of y + x4 to the power -1