Xiao Li and Xiao Gang are 900 meters away from home. They start from home at the same time. Xiao Li walks 60 meters every minute and Xiao Gang walks 90 meters every minute. A few minutes later, they meet?

Let two people meet after X clock. The equation is: 60x + 90x = 900
Solution equation: 60x + 90x = 900
150x=900
x=900/150
x=6
A: six minutes later, they met

Xiaoming and Xiaogang are 900 meters away from each other's home. They set out at the same time and face each other. Five minutes later, they met. Xiaogang walks 80 meters per minute. How much does Xiaoming walk per minute

900 △ 5 = 180m
180-80 = 100m

Xiaogang and Xiaoming set out from the two places at the same time. Xiaoming walked 80 meters every minute and Xiaogang walked 75 meters every minute. They met 10 meters from the midpoint

When they met, Xiao Ming walked 10 × 2 = 20 (meters) more than Xiao Gang
Xiaoming walks 80-75 more than Xiaogang every minute = 5 (meters)
Meeting time 20 △ 5 = 4 (minutes)
Distance between a and B (80 + 75) × 4 = 620 (m)
Comprehensive
10×2÷（80-75）×（80+75）
=4×155
=620 (m)

1. Given that a + 1 / a = 3, find the square of a + 1 / 2 of A. 2. Given that A-1 / a = 2, find the square of a + 1 / 2 of A. 3. Given that the square of A-B = 12, a + B = 6, find the value of the third power of algebraic formula A and the third power of b-ab. 4

1. A + 1 / a = 3
The square of a + a part = A & sup2; + A & sup2; part + 2 = 9
A & sup2; + A & sup2; 1 / 2 = 7
2. A-A 1 / 2 = 2
The square of A-A part = A & sup2; + A & sup2; Part-2 = 4
A & sup2; + A & sup2; 1 / 2 = 2
3. Square of a - square of B = 12, a + B = 6
The square of A-B = 2 (a-b) = A & sup2; + B & sup2; - 2Ab = 4
The square of (a + b) = A & sup2; + B & sup2; + 2Ab = 36 AB = 8
The value of the cubic power of a and b-ab = AB (A & sup2; - B & sup2;) = 8 * 12 = 96

On the calculation of pressure
There is a brick with a density of 2.5 × 10 ^ 3kg / m ^ 3, which can bear a pressure of 2.45 × 10 ^ 5pa. This kind of brick is stacked neatly on the horizontal ground which can bear 2 × 10 ^ 6pa. What is the maximum stacking height?
Think about it, don't understand -- explain it

The surface area of brick is s and the density is a
Because the ground can bear more pressure than brick, so the limit pressure of brick is the limit
Then the lowest pressure of the brick is just 2.45 × 10 ^ 5 PA
Then p = (ash × g) / S = 2.45 × 10 ^ 5 PA
H = 9.8m

Given the hyperbola x ^ 2-y ^ / 3 = 1, through P (2,1) point, make the intersection of hyperbola and a, B. if P is the midpoint of AB, find the linear AB equation

Point difference method, look at the picture! It's not complicated!

Can the diode be directly connected to 220 V AC?
I want to use four diodes to change 220 V AC into DC, how to operate

Not all diodes are OK! Diodes can be divided into many kinds according to their functions. First of all, you must use rectifier diodes. Not all rectifier diodes can rectify 220 V AC. rectifier diodes work at power frequency (50 Hz), so the requirement for response frequency is not very high

General score: 1 / 2x + 3,3 / 3-2x, 2x + 5 / 4 (x) square-9

Solution
The simplest common denominator is 4x & # 178; - 9 = (2x-3) (2x + 3)
∴
1/(2x+3)=(2x-3)/(2x-3)(2x+3)=(2x-3)/(4x²-9)
3/(3-2x)=-3/(2x-3)=-3(2x+3)/(2x-3)(2x+3)=(-6x-9)/(4x²-9)
(2x + 5) / (4x & # 178; - 9) unchanged

How to choose the wattage of energy saving lamp according to the room area?

At home, the walls are light
Bedroom, about 1.5 watts per square meter, light color 2700k or 3000K. Illumination about 200lx. To read a book, add about 40 watts of incandescent lamp, when reading, 2 to 3 meters away from this lamp
Living room, 2 to 2.5 watts per square meter, light color 5000K or 6400k. Illumination 250 to 300lx

(a + 1) (a ^ 2 + A / 2 + 1) and (a + 1 / 2) (a ^ 2 + A + 1)
ditto

(a + 1) (a ^ 2 + A / 2 + 1) = a ^ 3 + A ^ 2 / 2 + A + A ^ 2 + A / 2 + 1 (a + 1 / 2) (a ^ 2 + A + 1) = a ^ 3 + A ^ 2 + A + A ^ 2 / 2 + A / 2 + 1 / 2 by comparison, we can see that except for 1 and 1 / 2, all the others are the same and can be removed. (1 / 2 = 0.5) so it is wrong to get 1 > 0.5 = 1 / 2, the second floor

Xiao Li and Xiao Gang are 900 meters away from home. They start from home at the same time. Xiao Li walks 60 meters every minute and Xiao Gang walks 90 meters every minute. A few minutes later, they meet?