(1 / 4 + 0.75) / (2 / 2 1 × 0.4 + 1 / 5 4 / 1.8))

(1 / 4 + 0.75) / (2 / 2 1 × 0.4 + 1 / 5 4 / 1.8))

(1 / 4 + 0.75) / (2 / 2 1 × 0.4 + 1 / 5 4 / 1.8)
=（0.25+0.75）÷（2.5×0.4+1.8÷1.8)
=1÷（1+1)
=1÷2
=1 / 2

Let x1, X2 satisfy that X1 is not equal to X2, a > 0, Y1 = X1 / (1 + a) + AX2 / (1 + a), y2 = ax1 / (1 + a) + x2 / (1 + a)
What is the size relationship between x1x2 and y1y2

Let y1y2 / x1x2 = k, then
y1y2=kx1x2
(x1+ax2)(ax1+x2)=k(a+1)(a+1)x1x2
ax1x1+x1x2+aax1x2+ax2x2=k(x1x2+ax1x2+ax1x2+aax1x2)
Because x1x1 + x2x2 > = 2x1x2
So k > = 1, y1y2 > = x1x2

Use a 20 cm, 8 cm long ceramic tile to paste a square panel. If the square panel is just covered with complete porcelain, how many cm is the minimum side length of the square tile? How many such tiles are needed to paste it?
Use a 20 cm long and 8 cm wide tile to stick a square panel. If the square panel is just covered with complete porcelain, how many cm is the minimum side length of the square tile? How many such tiles do you need?

20. The least common multiple of 8 is 40
The minimum side length of a square is 40 cm
It needs 40 / 20 × 40 / 8 = 2 × 5 = 10 pieces

What is Kirchhoff's first law

Kirchhoff's first law: current node law. That is, in a period of time, the total current flowing into the node is equal to the total current flowing out of the node
Kirchhoff's second law: voltage loop theorem. At any time (note not a period of time), after running along the circuit for a week, return to the starting point, the voltage change rate is zero

X → 0 +, arcsinx * (1-x / x)

So Lim arcsinx * (1-x / x) = Lim x * (1-x / x) = Lim 1-x = 1

Cut a large square into eight identical millet cubes, each with a surface area of 18 square centimeters
What's the surface area of a square

The surface area of each cube is 18 square centimeters
Then one face of each small cube = 18 / 6 = 3 square centimeter
Cut a big square into 8 same millet cubes
That is to cut one knife in front and back, left and right, up and down, three in total
One face of a large square = four faces of a small cube
So one face of a large square = 4 × 3 = 12
Six faces 12 × 6 = 72
So the surface area of a large square is 72 square centimeters

Send the questions and see if they are the same as the math questions in my class

Is it: as shown in the figure, the line AB and CD intersect at point O, the angle EOC = 70 ° OA bisects the angle EOC, and calculates the degree of the angle BOD
If it is.
Answer: because: angle EOC = 70 ° OA bisector angle EOC (known)
So: AOC = 35 degrees
Also: angle AOC = angle BOD (equal to vertex angle)
So: the angle BOD = 35 degrees

Y = sin (x + y) for dy / DX
There is also an arctan Y / x = x / y to find the derivative

y=sin(x+y)
dy=cos(x+y)(dx+dy)
dy=cos(x+y)dx+cos(x+y)dy
dy/dx=cos(x+y)/(1-cos(x+y))

The circumference of a rectangle is 26cm. If the length of the rectangle is reduced by 1cm and the width is increased by 2cm, it will become a square. If the length of the rectangle is xcm, the equation ()
A. x-1=（26-x）+2B. x-1=（13-x）+2C. x+1=（26-x）-2D. x+1=（13-x）-2

Let the length of the rectangle be xcm, then the width is (13-x) cm. According to the equivalent relation: the length of the rectangle - 1cm = the width of the rectangle + 2cm, the equation is: X-1 = (13-x) + 2, so choose B

Paint the three same pillars, the perimeter of the bottom is 3.14 meters, the height of the pillars is 3 meters. Paint 0.5 kg per square meter, how many kg in total?

0.5x3.14x3x3 = 14.13kg