Mathematics, junior 3, urgent, junior 3 mathematics, urgent

Set up Xiao Wang ****x yuan.

The number of pounds per day is.

Take profit for. If 0=, the function f(y)=-200y 2+200y is obtained, and the maximum value is taken when y=.

x = y + oil price is set at yuan.

Set the price to be $x.

x[200-(multiplied by 20] multiplied by 20]=540 should be correct.

It's a quadratic equation...

Set the oil price at $x to make the biggest profit every day. （x=

Let the profit be y and the selling price be x. Then y=(,x's range is to. and y=200 (is a parabolic function. The two intersections with the x-axis are x=, so the range of x is monotonically increased at the time, so the profit is the largest when the price is fixed.

Solution: The set price is x, and it can be sold every day for y catties and make a profit of e yuan.

x—x—Convert the two equations into a quadratic equation about x and e, and find the fixed-point coordinates to get the maximum value of x.

Solution: Let the profit be y, and the oil price is **x

y=x*(200-20x/

There is a quadratic function curve. x=

Solution: 1) If the average annual growth rate of the family electric bicycle is x, then 125 (1 + x) = 180, the solution is x1 = , x2 = is not in line with the topic, and it is discarded).

180 (1 + 20%) = 216 (units), A: By the end of 2012, the community will reach 216 family electric bicycles;

So the team demolished 1,000 cubic meters on the first day.

Let this percentage be respectfully with x, then the first day of quiet demolition is 1000 (1+x), and the third day of demolition is 1000 (1+x) * (1+x) = 1000 (1+x) 2

So Lianglu, 1000(1+x) 2=1440 solution. x=20%

So this percentage is 20%.

560 + 560 (1 + x) + 560 (1 + x) 2 = 1850 560 in the first month, and x increased in the second month, then the tonnage of production in the second month is 560 (1+x).

The third month is multiplied by (1+x) times on top of the second month to get 560 (1+x) squared.

The three months add up to 1850

When the sun's rays are at an angle of 30° to the ground, the projection length l of Building A on the bottom surface is 20 (tan30°) = 20 * root number 3

Let the light be at the bottom of Building B at a height of h from the bottom of Building B.

h 20=(l-30) l=(20*root number 3-30) (20*root number 3)h=[(20*root number 3-30) (20*root number 3)] 20=20-10*root number3=20-10 approximately equal.

That is, the light is at the bottom of Building B and is at a height of meters from the bottom of Building B.

The bottom of the window is 2 meters from the bottom surface, so it covers part of the window, and the part that covers it is meters.

As shown in the figure, let the light affect the place of the building, as , from the inscription, then, then, because , so, that is, the shadow of the building affects the lighting on the first floor of the building, blocking the window meter of the household

Solution: Let the length of the two sides of the rectangle be a and b respectively, then 2a+2b=18, that is, a+b=91, when 5cm is the waist of an isosceles triangle.

The length of the base edge of the isosceles triangle is 8cm, and the height of the base edge can be obtained from the Pythagorean theorem, which is 3cm, and the area of the isosceles triangle is 8x3 2=12

The area of the rectangle is equal to that of the isosceles triangle.

The area of the rectangle = ab=12 and a+b=9 The rectangle side length a and b are (9+ 33) 2 and (9- 33) 22 when 5cm is the bottom edge of the isosceles triangle.

The waist length of the isosceles triangle is 13 2 cm, and the base height of the isosceles triangle is 6 cm from the Pythagorean theorem, and the area of the isosceles triangle is 5x6 2=15

The area of the rectangle = ab=15 and a+b=9 The rectangle side lengths a and b are (9+ 21) 2 and (9- 21) 2

The first case should be 5cm, the side length is the waist of the isosceles triangle, then the bottom is 8, and the isosceles triangle height can be 3

The triangle has an area of 12

Let the rectangle side length be x, y from the conditions in the problem.

xy=122(x+y)=18 Find x, y

In the second case, the side length of 5cm is the base of the isosceles triangle, then the waist is the height of the isosceles triangle is 6, and the area of the triangle can be obtained as 15, and the side length of the rectangle is a and b, which can be obtained from the conditions in the question.

ab=152(a+b)=18

Just out of the rectangular sides a and b

The 18 cm long wire is bent into an isosceles triangle with a side length of 5 cm.

Bottom edge 8 height 3 area 6

The side length of the rectangle is 3

Solution: Let the percentage be x

20（1+x）²

Solution: x1=

does not fit the topic, discard).

A: This percentage is 20%.

x(x-1)=2550

x^2-x-2550=0

x-51)(x+50)=0

x=51, x=-50 (not on topic, discarded).

A: There are 51 students in the class.

There are x people, each person should give x-1 x(x-1)=2550 to get x=51

If C is the high CE on the AB side, then 1 2AC*BC=1 2AB*CE (triangular area).

CE = 12 5 can be obtained

Use the Pythagorean theorem to find ae=9 5

ad=2ae=18/5

Connect cd, cd=ac=3, ab directly use the Pythagorean theorem, find out that it is 5, this problem seems to be not difficult, right?

From the problem, it can be seen that the angle c is 90°, ac=3 bc=4.

According to the Pythagorean theorem ab = root number AC + BC.

To connect the cd, it should be point d on the circle, so cd is equal to the radius of 3

The price of each shirt should be reduced by X yuan.

Derive the equation: (40-x)(20+2x) 1200 to solve this equation.

Because (40-x) represents the profit won by each piece of clothing per day after the price reduction (20+20x) represents the number of pieces that can be sold per day after the price reduction, where 20x represents the number of additional pieces bought per day after the price reduction, plus 20 is the total number of pieces sold per day after the price reduction!

Got it?? Schoolmate.

Set each piece should be reduced by x yuan, then after the price reduction, each piece will make a profit of (40-x) yuan, and can sell (20 + x * 2) pieces, with a profit of 1200 yuan, including:

40-x）*（20+2x）＝1200

Solve x 20 or x 10

Since only a price reduction of 1 yuan can be more **2 pieces, x 10 can only be more **16 pieces, which does not meet the requirements, so take x 20