How to solve the equation x + x-12.5 + 2x-12.5-25 = 130 fast

How to solve the equation x + x-12.5 + 2x-12.5-25 = 130 fast

4x-50=130
4x=180
x=45

The decimal parts of 9 + √ - 7 and 9 - √ - 7 are x, y, find 3x + 2Y
The decimal part of √ 7 and 9 - √ 7 is x, find 3x + 2Y

The concept of imaginary number is meaningless in real number field

There are two love teams, the number ratio of the first team to the second team is 5:3; after 14 people are transferred from the first team to the second team, the number ratio of the first team to the second team is 1:2, which turns out that the second team has two teams______ People

In the past, the number of the first team accounted for 5 (5 + 3) = 58; now the number of the first team accounted for 1 (1 + 2) = 13; the total number is 14 (58-13) = 14 (724, = 48); the number of the second team is 48 × (1-58) = 48 × 38 = 18; a: there were 18 people in the second team, so the answer is: 18

How many numbers are there in the 1000 natural numbers from 1 to 1000? What is the sum of all numbers
Example: 10 ~ 15 numbers and: 1 + 0 + 1 + 1 + 1 + 2 + 1 + 3 + 1 + 4 + 1 + 5 = 21
For example, the sum of 999 1000 is not 1000 + 999 = 1999, but 1 + 0 + 0 + 0 + 9 + 9 = 28
Urgent, quick answer! There must be a formula, and explain the reason! (clear)

There are several numbers: add 00 to the nine numbers [0] to 9, add 0 to the 90 numbers from 10 to 99, then from 000 to 999, these 1000 numbers are all "three digits", share 1000 * 3 = 3000, subtract 3 of the 000, and 9 * 2 + 90 * 1 = 108, add 10

A car from a city to B city, 3 hours form 240 kilometers, with the same speed and 1.2 hours to B city
(1) Find out the proportion of the two quantities in the paper and explain the proportion?

Time and distance are two proportional quantities, which are positively proportional, because speed (quotient of distance and time) is constant

In the Pentagon ABCDE, it is known that 2 angles a = angle D, 2 angles B = angle c + angle e, and the degree of angle a + angle B is calculated

Angle d = 2 angle a 2 angle B = angle c + angle e
So angle a + B + C + D + e = 3 angle a + 3 angle B = 720 degree
So angle a + angle B = 720 divided by 3 = 240 degrees

A car delivers goods to the mountain area, 42 kilometers per hour, 67 hours to arrive. It only takes 34 hours to return from the original road, how many kilometers per hour on average?

42 × 67 ÷ 34 = 36 × 43 = 48 (km / h). A: when returning, the average distance is 48 km / h

Try to compare the size of a and - A

When a ＞ 0, - a ＜ 0, so a ＞ - A; when a = 0, - a = 0, so a = - A; when a ＜ 0, - a ＞ 0, so a ＜ - A

An express train and a local train run in opposite directions. The length of the express train is 280 meters, and that of the local train is 385 meters. The time for people sitting on the express train to see the local train passing is 11 seconds, so the time for people sitting on the local train to see the express train passing is 11 seconds______ Seconds

The relative speed of the two trains is: 385 △ 11 = 35 (M / s); the time for people on the slow train to see the fast train passing is: 280 △ 35 = 8 (s)

Polar coordinates represent circles
For example, for a circle with (a, 0) as the center and a as the radius, why is ρ = 2acos θ?

Transformation of Cartesian coordinates and polar coordinates:
x=ρ*cosθ,y=ρ*sinθ,ρ^2=x^2+y^2
First write the equation of rectangular coordinates: (x-a) ^ 2 + y ^ 2 = a ^ 2
Expand: x ^ 2 + y ^ 2-2ax + A ^ 2-A ^ 2 = 0
That is: x ^ 2 + y ^ 2-2ax = 0
Conversion: ρ ^ 2-2a ρ * cos θ = 0
Same division: ρ - 2A * cos θ = 0
That is: ρ = 2A * cos θ