If the square of (a + 3) is + / B-2 / = 0, what is the value of ab - [2ab-3 (AB-1)]?

If the square of (a + 3) is + / B-2 / = 0, what is the value of ab - [2ab-3 (AB-1)]?

The square of (a + 3) ≥ 0, / B-2 / ≥ 0, but the sum is equal to 0
So a = - 3, B = 2
Just substitute the required formula
Original formula = - 6 - [- 12-3 (- 6-1)] = - 15

Three practical questions
1. A certain commodity is ready to be sold at a discount due to the change of season. If it is sold at a 25% discount, it will lose 25 yuan, and if it is sold at a 10% discount, it will earn 20 yuan. How much is the price of this commodity?
2. Xiao Ming goes from place a to place B at a speed of 30 kilometers per hour. If the speed increased by 30% per hour is more than 1 kilometer, it takes Xiao Ming two-thirds and 30 minutes to get to place B. what is the distance between a and B?
3. When a tailor makes one children's clothing, one pair of trousers and one coat, the ratio of all time is 1:2:3. He can make two children's clothing, three pairs of trousers and four coats in one day. How many days does it take for him to make two coats, 10 pairs of trousers and 14 pieces of children's clothing?

1. A certain commodity is ready to be sold at a discount due to season change. If it is sold at a 25% discount, it will lose 25 yuan, and if it is sold at a 10% discount, it will earn 20 yuan. How much is the price of this commodity? Suppose the price is X Yuan and the cost is a yuan. The equation is 0.75x-a = - 250.9x-a = 200.15x = 45x = 300 and the price is 300 yuan

If the side length of a square is increased by 5 meters, the area of the increased square is 95 square meters larger than that of the original square

The increased area is two rectangles with the original side length of 5 meters and one small square with the side length of 5 meters
So the area of a small rectangle is (95-5 * 5) / 2 = 35 square meters
The original side length is 35 / 5 = 7 meters
The original area is: 7 * 7 = 49 square meters

How to measure the distance between celestial bodies and the earth, the distance between celestial bodies?

Generally, the triangle method is used. For example, the earth observes the angle of a star to the earth at the vernal equinox and the autumnal equinox, and then calculates its distance from the earth with the radius of its orbit as the baseline
Trigonometric method is used to measure the distance of near objects (within 500 light years)
The distance of celestial bodies with 5-100000 light years is determined by photometry
Beyond 100000 light years, astronomers have found Cepheid variables as the standard, up to 500 million light years
The further distance is calculated from the observed redshift according to Hubble's theorem
Reference: the course of science by Wu Guosheng
There are different methods for the same celestial body distance
Astrometry Method
2.2.2 application of spectrum in astronomical research
People always want to know about the physical and chemical properties of celestial bodies. This desire is only possible after spectral analysis is applied to astronomy, which leads to the birth and development of astrophysics. Through spectral analysis, we can: (1) determine the chemical composition of celestial bodies; (2) determine the temperature of stars; (3) determine the pressure of stars; (4) determine the magnetic field of stars; (5) determine the apparent velocity and velocity of celestial bodies Rotation and so on
2.3 determination of celestial body distance
People always want to know how far the celestial body is from us, and the measurement of celestial body distance has always been the task of astronomers. Different methods can be used to measure different distant and near celestial bodies. With the development of science and technology, the means of measuring celestial body distance are more and more advanced, There are three kinds of astronomical distance units: astronomical unit (AU), light year (ly) and second gap (PC)
2.3.1 distance between the moon and the earth
The moon is the closest object to us. Astronomers have thought of many ways to measure its distance, It was not until the 18th century (1715-1753) that scientific measurements were made by the French astronomer N.L. Lacaille and his student larand using the trigonometric parallax method. Their results show that the average distance between the moon and the earth is about 60 times the radius of the earth, which is very close to the modern measurement value (384401km)
After the birth of radar technology, people use radar to measure the distance to the moon. After the advent of laser technology, people use the characteristics of laser, such as good directivity, concentrated beam, strong monochromatic to measure the distance to the moon. The measurement accuracy can reach centimeter level
2.3.2 distance between sun and planet
The orbit of the earth around the sun is ellipse, and the distance between the earth and the sun changes with time. Generally speaking, the distance between the sun and the earth refers to the semi major axis of the earth's orbit, which is the average distance between the sun and the earth. In astronomy, this distance is called an "astronomical unit" (1AU). In 1976, the International Astronomical Union set the value of an astronomical unit as 1.49597870 × 1011 meters, approximately 149.6 million kilometers
The sun is a hot gas sphere. The distance between the sun and the moon can not be measured directly by the trigonometric parallax method. In the early days, the distance between the sun and the moon was determined by the help of Mars or asteroids which are closer to the earth, In 1673, French astronomer Dominique Cassini measured the distance of the sun for the first time by taking advantage of the great impact of Mars
The distances of many planets are also calculated by Kepler's third law. If 1AU is taken as the distance between the sun and the earth, and "stellar year" is taken as the earth's revolution period, then T2 = A3. If the revolution period of a planet is measured, the distance between the planet and the sun can be calculated. For example, if the revolution period of mercury is 0.241 stellar year, then the distance between mercury and the sun is 0.387 astronomical units (AU)
2.2.3 distance between stars
Because stars are very far away from us, it is very difficult to measure their distances. Different methods should be used to measure the distances of stars at different distances
(1) Trigonometric parallax method
The distance between Hanoi celestial bodies is also called parallax. The angle of the average distance (a) between stars and the sun is called the trigonometric parallax (P) of stars
sinπ＝a/D
If π is very small, π is expressed in angular seconds, and the unit is the second gap (PC), then d = 1 / π
There are some limitations in measuring the distance between stars with the method of annual parallax, because the farther away the stars are from us, the smaller the π is, which is difficult to measure in practical observation. Trigonometric parallax is the basis of all celestial body distance measurement. So far, more than 10000 stars have been measured with this method
In addition to astronomical units (AU) and second gap (PC), there are also light years (ly), that is, the distance light travels in a vacuum in a year, which is equivalent to 9460.5 billion kilometers
One second gap (PC) = 206265 astronomical units (AU) = 3.26 light years = 3.09 × 1013km
1 light year (1y) = 0.307 second gap (PC) = 63240 astronomical units (AU) = 0.95 × 1013 km
(2) Spectroscopic parallax method
For more distant stars, such as stars more than 110pc away, because the annual parallax is very small, it can not be measured by trigonometric parallax method. Therefore, another convenient method, spectroscopic parallax method, has been developed. The core of this method is to determine the luminosity of stars according to the spectral line intensity of stars, and know the luminosity (absolute magnitude M), The distance can be obtained from the observed apparent magnitude (m)
m - M= -5 + 5logD.
(3) Distance measurement based on Cepheid's relationship
When the massive stars evolve to the late stage, they will show unstable pulsating phenomena and form pulsating variable stars. Among these pulsating variable stars, there is a kind of very regular pulsating period, which is called "Cephei" in Chinese. Cephei is the name of the ancient Chinese star official. One of the stars in the constellation δ is called "Cephei 1", It is a "variable star" whose brightness will change. There are many reasons for the light change of variable stars. Cephei 1 belongs to the category of pulsating variable stars. When its star expands, it appears brighter, and when its volume shrinks, it appears darker. This kind of brightness change of Cephei 1 is very regular, and its change period is 5 days, 8 hours, 46 minutes and 38 seconds, which is called "light change period", All variables that have the same changes as Cepheid one are collectively referred to as Cepheid variables
Author: haj520 2005-5-21 18:44 reply to this speech
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2 astrometric methods
In 1912, Leavitt (1868-1921), an American female astronomer, studied the magnitude and the period of light variation of Cepheids in the Small Magellanic galaxy, At present, more than 700 Cepheid variables have been found in the Milky way. The distance of many extragalactic galaxies is measured by this scale
(4) Red shift ranging method of spectral line
At the beginning of the 20th century, spectral studies found that almost all galaxies have red shift phenomenon. The so-called red shift refers to the observed spectral line wavelength (L) is longer than the corresponding laboratory measured spectral line wavelength (L0), and the wavelength of red light in the spectrum is longer, so the shift of spectral line to the direction of longer wavelength is called spectral red shift, In 1929, Hubble observed more extragalactic galaxies with a 2.5m telescope, and found that the farther away the galaxies are from us, the greater the redshift of their spectral lines
Hubble pointed out that the redshift of celestial bodies is related to distance: z = h * D / C, which is the famous Hubble's law, where Z is the redshift; C is the speed of light; D is the distance; h is the Hubble constant, whose value is 50-80 km / (s · M s). According to this law, as long as the redshift z of extragalactic lines is measured, the, The distance D of the galaxy can be calculated by redshift method

Calculation of scientific pressure density in grade two of junior high school
The side length of a cube metal block is 8 cm, which is placed on a horizontal board with an area of 100 square cm. The pressure generated by the metal block on the board is 6.125 * 10 cubic Pascal?

F = P * s = 6.125 * 10 to the third power PA * 64 * 10 to the - fourth power M2 = 39.2 n
m = G / g = F /g = 39.2 N / 9.8N/Kg =4 Kg= 4000g
Density of metal block = m / v = 4000 g / 512 cm3 = 7.8 g / cm3

The circumference of the bottom of a round vase is 12.56 cm, and its radius is______ Cm, the bottom area is______ Cm 2

The radius is: 12.56 △ 3.14 △ 2 = 2 (CM), the area is: 3.14 × 22 = 12.56 (square cm), answer: the bottom radius is 2 cm, the area is 12.56 square cm

Simple calculation of 15 × 23 × 4

15×23×4
=15×4×23
=60×23
=1380

Given TaNx = sin (x + π 2), then SiNx=___ ．

∵ TaNx = sin (x + π 2) = cosx, ∵ SiNx = cos2x = 1-sin2x, ∵ sin2x + sinx-1 = 0, the solution is: SiNx = 5-12 or SiNx = - 5-12 < - 1 (rounding off), so the answer is: 5-12

The ratio of side length to radius is (): (), and the ratio of square area to circle area is (): ()

For square and circle with equal perimeter, the ratio of side length to radius is (π): (2), and the ratio of square area to circle area is (π): (4)
If the side length of a square is a, then 4A = 2 π R, a: r = π: 2
The ratio of square area to circle area = π: 4

2,7,8,10, how to calculate equal to 24?

Really, if only add, subtract, multiply and divide, there is no answer
Thank you!