The solution equation: X △ 3 = 15

x=15×3
x＝45

Solution equation: (x + 2.5) * 4 = 15

（x+2.5）*4=15
x+2.5=15/4
x+2.5=3.75
x=3.75-2.5
x=1.25

How to solve the equation when 15-3 (x-1) = 6

15-3(x-1)=6
15-3x+3=6
3x=15+3-6
3x=12
x=4

A two digit number is a, and a ten digit number is 1 larger than A. what is the two digit number?

Let a be a third-order square matrix, the determinant | a | = 2, and a * be the adjoint matrix of a, then | (A / 4) ^ - 1 + A * | =? Solving process, online, etc```

A* = |A|A^-1 = 2A^-1
(A/4)^-1 = 4A^-1
therefore
|(A/4)^-1+A*|
= |4A^-1+2A^-1|
= |6A^-1|
= 6^3 |A^-1|
= 6^3/2
= 108

4 / 5 of a number is 18% more than 60% of the number. What is the number? (solve the equation)

Let this number be x, and we get
4/5x-60%x=18
0.2x=18
x=90

Composition on land desertification

Stop desertification in recent years, the news constantly broadcast that piece of fertile land in China, the original green covered land into barren land, so heartbreaking. Today's world has been constantly eroded by desertification land, this is an irreversible trend of development, of course, this is to human beings

Xiao Ming has a story book. He read 16 pages on the first day and 30% on the second day. There are still 45 pages left. How many pages of this book should we calculate
2. To produce a batch of toys, 20% of these toys will be finished in the first week, 25% in the second week, 400 more toys will be produced in the second week than in the first week, how many toys will be produced in total? 3. A 20% discount on the sales price of one kind of DVD player is 130 yuan cheaper than the original price. 4. How much is the original price of this kind of DVD player? A car has already made 60% of the whole journey from place a to place B, just 60 kg more than half of the whole journey, How many kilometers is the distance between a and B? 5 Xiao Ming read a book. On the first day, he read three pages less than one tenth of the whole book. On the second day, he read 48 pages. In two days, he read a total of 40% of the whole book. How many pages is this book

1. (16 + 45) / (1-30%) = 610 / 7 pages
2.400/（25%-20%）=8000g
3.130/（1-80%）=650
4.60/（60%-50%）=600
5. Let x page (x / 10) - 3 + 48 = x * 40% x = 150

Let all integers which can be expressed as the sum of the squares of two integers be denoted as m, and try to prove that the product of any two elements of the set m still belongs to M
The process should be detailed

The distance between the two cities is 580 km. The freight cars drive from Yicheng to Jiacheng at the speed of 68 km per hour. Half an hour after the freight cars leave, the passenger cars leave Jiacheng
Go to city B, meet the truck in 4 hours. Find the speed of the bus. Use the equation

Let the speed of the bus be X
68×0.5+（68+x）×4=580
340+4x=580
4x=240
x=60
A: the speed of the bus is 60 km / h

The solution equation: X △ 3 = 15