Mathematics 3rd year: 1 problem, 1st junior high school math problem

Because be=ad=bc=5, ab=3, so ae=4, so ed=ad-ae=5-4=1

Because cd=ab=3

So EC = CD square under the root number + ED squared = root number 10 from B like EC to make a perpendicular line, and EC intersects at point F.

Because be=bc=5

So the triangle BEC is an isosceles triangle.

So ef = 1 2 ec = 1 2 root number 10

First of all, the area of the triangle BEC = 1 2 * be * ec * sin bec

ab=3, be=ad=5, from the Pythagorean theorem, calculate ae=4, then ed=5-4=1, dc=3, and then from the Pythagorean theorem, calculate ec=root number 10;

The area of the triangle bec is half the area of the rectangle, that is, 15 2 substituting the above equation, and calculating sin bec = (3 * root number 10) 10

Because it is an ABCD rectangle, AD=BC, AB=CD, AB is perpendicular to AD Because AD=5, AB=3, BE=AD, so DC=AB=3, BE=BC=5, and the triangle EBC is an isosceles triangle Crossing the point b as bf perpendicular to ec and ec in f ef=fc By the Pythagorean theorem ae=4, ed=1, ec=root10, ef=1 2 (root10), bf=3 2 (root10), sin(bec)=3 10 (root10)

It is easy to calculate that the length of ae is 4, because ad is equal to be, that is, ad is equal to bc, and be is equal to 5, then ae ab be's pythagorean theorem can obtain ae, then ed is equal to 1, and the pythagorean theorem again obtains ce equal to the root number 10, use the cosine theorem to obtain the cosine value of the angle obtained, and then use the sine cosine relation to obtain the sine value!

Since be=ad=bc=5

Then the triangle BEC is an isosceles triangle.

ae=(be*be-ab*ab)1/2=4sinabe=ae/be=4/5=

abe = degrees.

bec=90-∠abe=90-53=37°sin∠bec=sin37°=

Among them, I don't know if you can understand the knowledge of the afterstrings of rice.

If you calculate the above and then calculate it, I think it will be more troublesome, I hope it can help you.

The latter round of a single round-robin tournament was played 33-3=30 games, and the equation x(x-1) 2=30 was solved to obtain a total of 6 teams in the latter round. So there were 12 detachments in total.

The title is wrong.

In the round-robin tournament, each team is (x-6-1) but has an overlap, which should be divided by 2x*3+(x-6)(x-6-1) 2=33x=

There are x teams, and n teams need a total of 1+2+ ...... in a single round-robinn-1) Actually, this is also a combination problem, I don't know if you have learned it, so 3x 2 + x-6-1)(x-6-1+1) 2 = 33, the solution is x=10 or -2 (rounded).

What does a single round robin mean? Don't understand???

Reason for choosing A:

By the intersecting string theorem: Pa*pb=pc*pd, 3*4=6pd, pd=2, by the cutting wire theorem: ea 2=ec*ed

2√5)^2=ec(ec+cd)

20=ec(ec+8), the solution yields ec=4

Answer] The average is 3 times 2 + 5 = 11 (process omitted) type Jinsun.

The variance formula is the chain: k 2s = 3 2 * 6 = 54

ab=3 Because the two triangles are similar, ad ab=de bc

So bc=

Because de bc, so the angle ade = angle abc, known by similarity, ad ab = de bc ab = ad + db = 3 so bc = substitute a calculation).

Do OE CD to E, connect OC, OD

Because oa=ob

So ae=be

oc=od again

So ce=de

ac=ae-ce, db=be-de

So ac=db

The O point is made as OE perpendicular to CD

Because OA=OB and OE is a common edge, AE=BE is obtained by the Pythagorean theorem, and because OE bisects CD, CE=DE

So ae-ce=be-de

This gives us ac=db

Suppose it is x people, then the number of people infected after the first day is x+1, the second day is x*(x+1)+x+1, and the third day is x*(x +2x+1)+x +2x+1=9 So the cubic of x+1 is equal to 9. x

In this way, the law can be deduced, and after three days, that is, six days later, that is, the sixth power of x+1 is equal to 81

So, three days later, a total of 81 people were infected.

Solution: Let the average person infect x people per day on average, and get the following from the question

x+1+x(x+1)=9

Solution: x1 = 2, x2 = -4 (not in line with the topic, discarded) So on average, each person infects 2 people per day.

So the total number of people infected after 3 days is: 9 (x+1) = 27 (people).

With the inference algorithm: one person can infect 2 people a day. A total of 8 people were infected in 3 days, and a total of 9 people were infected with the original infection.

The law is (2 n)+1, where n is the number of days.

So 9 people infected a total of 9 [(2 3)+1] 81 people after three days.