How to solve this equation is 2 * [x + 19] = 43

2X+38=43
2X=43-38
2X=5
X=5/2

Find the positive integer solution of equation (1 / x) + (1 / x + 1) + (1 / x + 2) + (1 / x + 3) = 19 / 20

If x is a positive integer, first look at the range, the left side is less than 4 / X and greater than 4 / (x + 3). First solve the equation 4 / x = 19 / 20, and get x = 4.2
If 4 / (x + 3) = 19 / 20, x = 1.2
Then the range of positive integer solution is 1.2 ≤ x ≤ 4.2
The possible values of X are 2,3,4, each of which is taken into account, and the final solution is x = 3

The essence of solving function range by analytic formula method
For example, find the range of y = 2x ^ 2 + 2x + 3 / (x ^ 2 + X + 1)
The formula (Y-2) x ^ 2 + X (Y-2) + Y-3 = 0
When y = 2, - 1 = 0, round off
When y ≠ 2, let △≥ 0 and find 2 ＜ y ≤ 10 / 3
What is the basis for doing this? Why is the value range of the original function obtained by making the discriminant greater than or equal to zero? Please explain the essential reason

Y = 2 is a linear equation about X
Y ≠ 2 is a quadratic equation about X. if the equation has a real number solution, then the discriminant △≥ 0, so that X has a real number solution and X has a real number solution. Substituting into the original equation, y has a real number solution

X tends to 0 to find the limit of 1 / Sin & # 178; X-1 / X & # 178

First, general division, then Equivalent Infinitesimal Substitution, and then use the law of lobita three times, finally equal to 1 / 3
=lim(x²-sin²x)/x²x²=lim(2x-2sinxcosx)/4x^3=lim(2-2cos2x)/12x²=lim4sin2x/24x=1/3

The perimeter of a rectangular vegetable field is 200 meters. If the length of the vegetable field is increased by two fifths and the width by one fourth, how much is the area increased?

Area increase = (1 + 2 / 5) × (1 + 1 / 4) - 1 = 3 / 4

Jiangsu Education Press sixth grade volume II mathematics evaluation manual midterm test answers urgent!

1.2.3 5050.188235
2.6 60 75 12 0.75
3. One fifths: one fifths: eight fifths: eight fifths
four point one five six
5. Three fifths
6. No bottom perimeter
7.1：40000000 3.5
8.5 4
9.7.5
ten point eight
eleven point two one
12. Positive 450
(2) 1. ② 2. ① 3. ③ 4. ① 5. ④

General solution of DX + (x + y ^ 2) dy = 0

∵dx+(x+y^2)dy=0
==>E ^ YDX + Xe ^ YDY + y ^ 2E ^ YDY = 0
==>e^ydx+xd(e^y)+y^2e^ydy=0
==>d(xe^y)+d((y^2-2y+2)e^y)=0
==>Xe ^ y + (y ^ 2-2y + 2) e ^ y = C (C is a constant)
==>x=Ce^(-y)-y^2+2y-2
The general solution of the original equation is x = CE ^ (- y) - y ^ 2 + 2y-2

There are two square tablecloths, both of which are 1 meter long. The little celebrity bought a square tablecloth with a side length of 1.3 meters, which can't be thrown away. How to make it into a proper size, unexpectedly, it can't be left. (it's better to have pictures than words without pictures,

Sorry, I'm in grade six. Give me an example. I don't know the title

The lobby of a hotel has 6 large cylindrical columns, 10 meters high and 25.12 decimeters in circumference. All the columns should be painted. If the painting fee per square meter is 80 yuan, how much will it cost?

25.12 decimeters = 2.512 meters, the total area to be painted: 2.512 × 10 × 6, = 150.72 (square meters), 150.72 × 80 = 12057.6 (yuan); answer: the total cost of painting these columns is 12057.6 yuan

How to fill in the operation symbols between 1.2.3.4.5?

5-4+3-2-1=1

How to solve this equation is 2 * [x + 19] = 43