The density of oxygen contained in a steel cylinder is 8kg / m3. If 1 / 4 of oxygen is used in one welding, the density of residual oxygen in the cylinder =?

It should be 6kg / m3

It is defined that △ is a new operation, a △ B = 3a-2b, for example, 4 △ 2 = 3x4-2x2, 1 / 2 △ 1 / 3 = 3x1 / 2-2x1 / 3. It is known that x △ 4 △ 1 = 7 is the value of X
I typed x as a multiply sign

First calculate 4 △ 1 to get 10, then bring in the formula x △ 10 = 7 3x-2 × 10 = 7 to get x = 9

Ask a math problem,
A bus starts from station a, passes through station B and C, and finally arrives at station d. There are (9a + 8b + C + 2) people on the bus when it starts from station a, and one third of the original number of people get off at station B. the number of people getting on the bus is one more than two-thirds of the number of people getting off at this station. When the bus passes station C, the number of people getting on the bus is two more than the number of people getting off. The number of people on the bus when it arrives at station D is calculated

Number of passengers on the train when arriving at station D: (9a + 8b + C + 2) * 2 / 3 + [(9a + 8b + C + 2) * 1 / 3 * 2 / 3 + 1] + 2
=（9a+8b+c+2)*8/9+3

Light year is the unit of distance used in astronomy, which is mainly used to measure the distance of celestial bodies outside the solar system. 1 light year refers to the period of time that light experiences in a vacuum?
Light year is the distance unit used in astronomy, which is mainly used to measure the distance of celestial bodies outside the solar system. 1 light year refers to the distance% d% a that light travels in a vacuum for one year. Today, the depth of the universe observed by human beings has reached 15 billion light years. Can you calculate how many kilometers this distance is equal to? (known light speed is about 3x10 of 2 cubic km / s)

C language: Calculation of PI
Description
According to the following relation, find the value of PI until the value of the last term is less than epsilon.epsilon The value of is entered by the keyboard
pi/2=1+1/3+2!/(35)+3!/(357)+...+n!/(3537...(2n+1))
Input
Enter a floating-point number to represent the value of epsilon
Output
Output pI value, keep 6 decimal places
Sample Input
zero point zero zero zero zero zero one
Sample Output
three point one four one five nine zero
HINT
(Reference: when epsilon is 0.01, PI is 3.121501; when epsioon is 0.0001, PI is 3.141358)

#include<stdio.h>int main(){ int n; double e,f,fz,fm,sum,pi; n=0; fz=1; fm=1; sum=0; scanf("%lf",&e); for(f=1;f>=e;n++) { if(n==0) fz=1; else fz=fzn; fm=fm(2n+1); f=fz/fm; sum=sum+f; } pi=2sum; printf("%.6f\n",pi); return 0;}
But turn in is wrong answer, and the last decimal point of my answer is 1. Hope to help me see what's wrong

Add a sentence after the for loop: sum - = f;
You added the last value less than epsioon

2. There is a cylinder whose bottom area is exactly equal to the side area. If the bottom area of the cylinder remains unchanged, its height will be increased by 2 cm,
Its surface area is increased by 94.2m. What is the original surface area of this cylinder?

Bottom circumference = 94.2 △ 2 = 47.1cm
Radius = 47.1 △ 3.14 △ 2 = 7.5cm
Bottom area = 3.14 × 7.5 × 7.5 × 2 = 353.25 square centimeter
Surface area = 353.25 × 2 = 706.5 square centimeter
Because the side area is equal to the bottom area
If you understand and solve your problem,

Given that the x power of 2 is equal to 3 and the Y power of 2 is equal to 5, then what is the 3x-y power of 2 equal to?

If a is an integer, then a & # 178; + a must be divisible by several integers

2
If a & # 178; + a = a (a + 1), a is an integer, one of a and a + 1 must be odd and the other even, then a & # 178; + a must be divisible by 2
It is impossible to judge whether it can be divided by other numbers
First hit,

The focus of the ellipse X & # 178 / 9 + Y & # 178 / 2 = 1 is F1F2, and the point P is on the ellipse. If | Pf1 | = 4, the size of the angle f1pf2 is

|PF1|+|PF2|=2a=6
|PF1|=4
|PF2|=2
cos∠F1PF2=（|PF1|²+|PF2|²-4c²）/2|PF1||PF2|
=(16+4-28)/(2*4*2)
=-1/2
∠F1PF2=120°

The reciprocal sum of two different prime numbers is 24 / 143. What is the reciprocal of the sum of the two prime numbers?

143=11×13
therefore
The two prime numbers are 11 and 13
therefore
Original formula = (11 + 13) 1 / 24 = 1 / 24

The density of oxygen contained in a steel cylinder is 8kg / m3. If 1 / 4 of oxygen is used in one welding, the density of residual oxygen in the cylinder =?