Use the four numbers 1, 3, 7 and 8, and use +, -, *, /, () to form the formula of the number 24

Use the four numbers 1, 3, 7 and 8, and use +, -, *, /, () to form the formula of the number 24

3 ÷ (1 - 7 ÷ 8)
(7 - 1 - 3) × 8

What's the formula of the number 24 composed of 4, 4, 10 and 10

﹙10×10-4﹚÷4=24

Define a kind of operation "△" to satisfy the following conditions: 8 △ 2 = 8 + 9 = 17,5 △ 3 = 5 + 6 + 7 = 18,4 △ 6 = 4 + 5 + 6 + 7 + 8 + 9 = 39, find the calculation results of 7 △ 3 and 1 △ 100
I hope it can be more detailed

8 △ 2 means that starting from 8 and then adding continuously, including 8, plus two digits, is 8 + 9 = 17
5 △ 3 means that starting from 5 and then adding continuously, including 5 and adding three digits, is 5 + 6 + 7 = 18
1 △ 100 means to add from 1 to 100, including 1 and 100 digits
That is, 1 △ 100 = 1 + 2 + 3 +. + 98 + 99 + 100 = (1 + 100) × 100 △ 2 = 5050
By hand,

How to solve 20x = 40-10x by equation

20x=40-10x
20x-10x=40
10x=40
x=4

Is the distance between a point on an ellipse and two focal points equal to the length of two major axes 2A
a

You are right!
Ellipse definition: the trajectory of a point whose distance from a point to two points on the plane is a fixed value is an ellipse
Therefore, the sum of the distances from any point on the ellipse to the two focal points is 2a, and a is the length of the major axis of the ellipse

The general term formula of sequence 3 5 9 17

an = 2^n + 1 ,n=1,2,3.
It's the nth power of two plus one

-3x & # 178; + 360x-9600 = 1200, solve the equation

-3x²+360x-10800=0
x²-120x+3600=0
(x-60)²=0
x1=x2=60

Seven centimeters is a fraction of a decimeter

Seven tenths of a meter seven hundredths of a meter

(1 and 13:8 × 42:13 + 6:1 and 2:1) / (11-1 and 2:3) how to calculate it simply

(1:13 of 8 × 42:13 + 6:2 of 1) / (11-1:3 of 2)
=(21/13×13/42+13/2)÷28/3
=7×3/28
=3/4

The solution steps of simple equation: ① for the equation with one-step operation, it can be solved according to () of addition, subtraction, multiplication and division; for the equation with two or three-step operation, it can be determined according to () first, and then ()

First empty fill inverse operation
The second empty operation order
Simplified solution of the third empty filling