It is known that the function f (x) is an even function defined in the interval from negative infinity to positive infinity. When x belongs to the interval from negative infinity to 0, FX = X

When x belongs to the interval 0 to positive infinity, FX = - X

Formula for solving quadratic equation of three variables
Case x + 2Y = 5
2X-3（X-Y）=10

2x-3x+3y=10
3y-x=10
And X + 2Y = 5, x = 5-2y
3y-5+2y=10
5y=15
y=3
x=-1

Father and son plant trees on the mountain. Father plants trees for 20 hours and son plants trees for 8 hours. They plant 396 trees in total. If the trees planted by father in 4 hours are equal to those planted by son in 5 hours, how many trees do they plant each hour? (arithmetic required)

If 5 / 4 = 1.25, 8 / 1.25 = 6.4 and 8 / 1.25 = 1.25, 8 / 1.25 = 6.4, 8 / 1.25 = 6.4, then 396 / (20 + 6.4) = 15 trees per hour for father and 15 / 1.25 = 12 trees per hour for son

Simple calculation of fraction (5 / 6-5 / 9) × 18 / 5

（5/6-5/9）×18/5
＝5/6×18/5-5/9×18/5
＝3-2
＝1

The original price of Andersen's fairy tales is 24 yuan, and the current price is 4 yuan cheaper than the original price. How much lower is the current price?

The current price is lower than the original price: 4 / 24 = 1 / 6

100+90+80+70+60+50+40+30+20+10-30

550-30=520

Given that x plus y is equal to 3, then the value of 9 minus 2x minus 2Y is

It is known that x + y = 3,
9-2X-2Y=9-2(x+y)=9-6=3

Sentences that explain things
A little more, to explain things purely
It's a sentence, a little shorter
Anything will do

In summer, when the rain is over and the sky is clear, a colorful arc is often hung on the cloud screen opposite the sun
Uranium is a silver white metal,
The "death" here refers to the death of fish, shrimp, plants and plants. Because the salinity of death is very high, organisms can not grow, so it is called "Dead Sea", which partly reveals the characteristics of the dead sea
"The branch is built on the company" ensures our party's absolute leadership over the army, which is Mao Zedong's most concise interpretation of Marxist Party building theory

Is 2100 a leap year? How to judge a leap year

2100 is not a leap year. The method of calculating a leap year is to divide the year by 4, and the result is an integer, that is, the year is a leap year, but the year points ending with 00 should be divided by 400, and the same result is the certificate. For example, 1994 / 4 = 499, then 1994 is a leap year, while 2000 / 400 = 5, then 2000 is a leap year, but 2100 / 400 = 5.25, so 2100 is not a leap year

1.2.3.4.5.6.7.8.9. How to calculate that the horizontal, vertical and oblique are equal to 15?
It's nine digits. It's a square

4 9 2
3 5 7
8 1 6

It is known that the function f (x) is an even function defined in the interval from negative infinity to positive infinity. When x belongs to the interval from negative infinity to 0, FX = X