(1 / 7-1 / 9) × 63-2 / 3, 8 / 15 × [3 / 4 + (7 / 16-1 / 4)] (1 / 7-1 / 9) × 63-2 / 3, 8 / 15 × [3 / 4 + (7 / 16-1 / 4)] (9 / 8-1 / 3) / (7 / 18 × 2 / 3) (process)

(1 / 7-1 / 9) × 63-2 / 3, 8 / 15 × [3 / 4 + (7 / 16-1 / 4)] (1 / 7-1 / 9) × 63-2 / 3, 8 / 15 × [3 / 4 + (7 / 16-1 / 4)] (9 / 8-1 / 3) / (7 / 18 × 2 / 3) (process)

1. (1 / 7-1 / 9) × 63-2 / 3 = (9-7) - 2 / 3 = 2 / 3 = 42 / 3, 8 / 15 × [3 / 4 + (7 / 4 / 16)] = 8 / 15 * [3 / 4 + (7 / 16-4 / 16)] = 8 / 15 * (3 / 4 + 3 / 16) = 8 / 15 * (12 / 16 + 3 / 16) = 15

5 × 6 / 1 + 6 × 7 / 1 + 7 × 8 / 1 + 8 × 9 / 1 + 9 × 10 / 1
The method is simple and convenient

=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1/5-1/10
=1/10

11+13+17+19=()*()=() 11++13+17+19+21=()*()=() 3+6+9+.+99=()*()=() 1+4+7+.+100=()*()=()
101+103+105+.+199=()*()=()
Please give the answer and explain the rules,

The problem of arithmetic sequence
(first plus half of last) * (quantity)

Given that real numbers x and y satisfy x2 + y2 = 4, the value range of X + y is obtained

What grade? What knowledge have you learned? This problem can be solved by algebra, geometry and triangle
All for your reference
(1) Pure algebraic method
Because (x + y) &# 178; = x & # 178; + 2XY + Y & # 178; = 4 + 2XY ≤ 4 + X & # 178; + Y & # 178; = 8
So - 2 √ 2 ≤ x + y ≤ 2 √ 2 equal sign is obtained when x = y
(2) Plane geometry method
Because X & # 178; + Y & # 178; = 4, a right triangle can be constructed so that the two right sides are x and Y respectively, and the hypotenuse is 2
Then the knowledge of plane geometry knows that when the hypotenuse of a right triangle is a fixed value, then the sum of the two right angles is equal, there is a minimum value
If the hypotenuse is 2, then when x = y = √ 2, the minimum of X + y is 2 √ 2
Considering that X and y can be negative in the original problem, it is concluded that
-2 √ 2 ≤ x + y ≤ 2 √ 2 equal sign is obtained when x = y
(3) Trigonometric function method
Since X & # 178; + Y & # 178; = 4, let x = 2cost, y = 2sint,
Then x + y = 2 √ 2Sin (T + π / 4)
Because - 1 ≤ sin (T + π / 4) ≤ 1
It is concluded that
-2 √ 2 ≤ x + y ≤ 2 √ 2 is obtained when t = π / 4, i.e. x = y

The number of students in the fifth grade is 3 / 4 of their age. How many students are there in each grade? (solution of the equation)
No bivariate!

There are X students in Grade 6
3X/4+X=371
7X/4=371
X=371*4/7
X=212
Grade 5 = 212 * 3 / 4 = 159
Do not understand can ask, help please adopt, thank you!

The square root of 22.5 × 240 =?

Root sign (22.5x240) = root sign (225x4x6) = root sign (900x6) 30 times root sign 6

The number a is five sixths of the number B, the number B is two-thirds of the number C. what are the numbers a, B, C and 200 respectively

Take number C as unit 1, number B is 2 / 3, and number a is 2 / 3 × 5 / 6 = 5 / 9
The number of C is: 200 (1 + 2 / 3 + 5 / 9) = 90
The number B is 90 × 2 / 3 = 60
The number of a is 90 × 5 / 9 = 50

Can X be the denominator in the equation
Hurry up. I'll give you a reward of 20

Look at the question you asked, it should be a primary school student
Pupils should try to avoid using X as the denominator
If x appears on the denominator, it is not a linear equation with one variable
It's a fractional equation. I'll learn it in junior high school

The greatest common factor of a and B is 5, and the least common multiple is 120. Given that a is 40, then B is 40______ ．

120 × 5 / 40, = 600 / 40, = 15; answer: B number is 15; so the answer is: 15

2X & # 178; + X-6 = 0, find x =?

X has two results, one is - 2 and the other is 3 / 2