Math genius comes, math genius comes

1.Solution: If we know that the speed of a boat in still water is 10 and the river velocity x and the total distance is y, then the system of equations y = 6 ...... can be listed according to the problem1）

y/（10-x）=9 ……2）

1) (2)=(10-x) (10+x)=6 9 x=2km h

Question 2: Departing from the bottom of a 36-storey building. When A goes to the 6th floor. B to the 5th floor Let A walk to the 6th floor takes a unit of time Then 36 6 = 6 A takes 6 units of time, in 6*5=30 B to the 30th floor But this should not be right, A walked to the 6th floor in a unit of time, but A actually walked 5 floors from the first floor to the 6th floor It should be 36 5*4= This is not an integer It should be 28 I don't know if the question starts from the bottom of the 36-story building is from the first floor or from the basement?

Question 3 A and B set off in AB and two places. B: Before A, after finding how much time A catches up with B, the meaning of this problem should be to go in the same direction, let the distance of ab be s, the speed of A is set to x, then x=s 12 Let the speed of B be y=s 15 When t time passes and A catches up with B, then t=s (x-y) substitute xy into the rounding of s, t=60

Question 4 A car is 180 meters long. B, the length of the car is 260 meters, then the total distance is s=180+260=440 meters, and the total speed of the car in the direction of the phase is v=20+24=44m/s, and st=10 seconds.

Question 5 Moving the train at a constant speed. It takes 18 seconds to go from a 320-meter tunnel to a complete tunnel Set the train length s The train speed v=(320+s) 18 A fixed light on the top of the tunnel shines on the train for 10 seconds, that is, the train walks a train length in 10 seconds v=s 10 substitute v=s 10 into v=(320+s) 18 and find s=400 meters.

Give it to me, I'm typing so hard.

Question 1 If we know that people are moving in still water, we set the river speed x and a certain water distance is y, then we can list the equation y = 6 according to the meaning of the problem

y (v-x)=9.

Question 2: Departing from the bottom of a 36-storey building. When A goes to the 6th floor. B to the 5th floor Let A walk to the 6th floor takes a unit of time Then 36 6 = 6 A takes 6 units of time, in 6*5=30 B to the 30th floor But this should not be right, A walked to the 6th floor in a unit of time, but A actually walked 5 floors from the first floor to the 6th floor It should be 36 5*4= This is not an integer It should be 28 I don't know if the question starts from the bottom of the 36-story building is from the first floor or from the basement?

Question 3 A and B set off in AB and two places. B: Before A, after finding how much time A catches up with B, the meaning of this problem should be to go in the same direction, let the distance of ab be s, the speed of A is set to x, then x=s 12 Let the speed of B be y=s 15 When t time passes and A catches up with B, then t=s (x-y) substitute xy into the rounding of s, t=60

Question 4 A car is 180 meters long. B, the length of the car is 260 meters, then the total distance is s=180+260=440 meters, and the total speed of the car in the direction of the phase is v=20+24=44m/s, and st=10 seconds.

Question 5 Moving the train at a constant speed. It takes 18 seconds to go from a 320-meter tunnel to a complete tunnel Set the train length s The train speed v=(320+s) 18 A fixed light on the top of the tunnel shines on the train for 10 seconds, that is, the train walks a train length in 10 seconds v=s 10 substitute v=s 10 into v=(320+s) 18 and find s=400 meters.

Give it to me, I'm typing so hard.

Question 1, just know this:

v (speed with the water) + v (speed against the water) = 2v (boat speed).

v (velocity against the water) - v (velocity against the water) = 2v (velocity of the water).

First, after finding the derivative of the cubic function, it is equal to 0, and the solution obtains that x = under the positive and negative root signs (b 6a);

According to its derivative image, it is judged that the negative value is taken.

However, since x has a range, the global maximum value of the cubic function cannot be obtained.

So there are two cases, the first is when x=0, and 1 is under the positive root sign (b 6a), according to the second-order guide image, the maximum value is obtained at 0, so max f(x)=b-a;

Second, when the root number of 1> is positive (b 6a), the maximum value may be (not necessarily, because the increase or decrease is not necessarily, but it is certainly not at 0 or at 1 point), and this second-order guide can be seen when it is drawn. When x=1, the maximum value is 3a-b. The first question is solved.

The second question is based on the first question, and I changed it a little, and I knew the maximum value, as long as I ensured that the maximum and minimum values were within a given range, I wouldn't do it.

Hope it helps

Can you be more elaborate?

Perimeter meter radius meter area =

Square metre.

The picture is good, but the topic is on the simple side.

Radius r=circumference 4 semicircles = 2 circles = 2x2 r= m

Area: 4 semicircles + middle square = 2x r square + m2

The circumference is the circumference of two circles: 2*

The area is the area of two circles + the area of a square with sides of the length: =2*

Circumference = 2 circles = 2 * d = 2 * =

Area = Two circles + one square = 2 r2 + d 2 = 2 += +

s 2 circles plus a square Adopt ah.

The area and perimeter are both 2 circles, the area formula of a circle is r 2 , and the perimeter formula is 2 r r=

Solution: Set x and y people from group A and group C, and set equation 3 (15-x) = 10 + x + y according to the problem

25-y+20=10+x+y

Solve the system of equations and get: x=5 , y=15

A: 5 people will be selected from Group A and 15 people will be selected from Group C.

Set up x people from group A and y people from group C.

Then: 10+x+y=3(15-x).

10+x+y=（25-y）+20

That is: x+2y=35....1)4x+y=35...2) (2) 2-(1) get:

7x=35x=5y=15

After the adjustment, B is 3x, A is x, C is 3x-20, and the number of people after adjustment and before adjustment is equal to give an equation 3x+x+3x-20=15+10+25

Solution x=10, 10 people after adjustment, so the drawn A is 15-10=5. Do the rest.

After adjustment, A, B, C, is.

5 people from Group A and 15 people from Group C.