If the length of a rectangle is reduced by 5cm and the width is increased by 2cm, it becomes a square, and the areas of the two images are equal?

If the length of a rectangle is reduced by 5cm and the width is increased by 2cm, it becomes a square, and the areas of the two images are equal?

Let the length be x and the width be y, then
X-5 = y + 2, that is, x = y + 7
(X-5) (y + 2) = XY, which is reduced to 5Y + 10 = 2x
By solving the system of equations, we get
x=25/3,y=4/3
So, this rectangle is 25 / 3cm long and 4 / 3cm wide,

In triangle ABC, angle c = 55 ° and angle B = angle A-35 ° to find angle A

∵A＋B＋C＝180°
C=55°
∴A＋B＝125°
Angle B = angle A-35
∴A＋A－35°＝125°
∴2A＝160°
A＝80°

With people's increasing awareness of environmental protection, water-saving sanitary ware has gradually entered people's families. The so-called water-saving sanitary ware refers to the sanitary ware whose water consumption is less than 6L each time. A family has newly installed a set of water-saving sanitary ware whose water consumption is 5L, while the original sanitary ware's water consumption is 9L each time? (the density of water is 1.0 × 103kg / m3) (2) how many kg of water can the family save per month? (set an average of 10 times per day, 30 days per month)

(1) The results show that the water consumption of new sanitary ware is M1 = ρ V1 = 1.0 × 103kg / m3 × 0.005m3 = 5kg; the water consumption of 1000kg is n = MM1 = 1000kg / m3, 5kg = 200 (Times). (2) the water saving volume of the family is v = 9l-5l = 4L = 0.004m3; the water saving quality is M2 = ρ V2 = 1.0 × 103kg / m3 × 0.004m3 = 4kg

Use a 40cm long iron wire to form a rectangle. If the area of the rectangle is 75cm2, how much is the width?

Let the width be x and the sum of length and width be 20, then the length is 20-x
Then x (20-x) = 75
The solution is x = 5, x = 15
The analysis shows that
The width is 5 and the length is 15

It is proved that 2 to the fifth power of 2 plus 1 is a composite number
Let me know by tomorrow

2 to the fifth power of 2 plus 1 = 1025
Obviously 1025 is divisible by 5, so it's a composite number of course

There is an urgent need for the calculation of the addition and subtraction of fifth grade mathematics scores. The equation is OK, and the difficulty is moderate,
Textbook is the people's education press fifth grade mathematics volume II, 30 ~ 50 can. (if there is no time, 10 ~ 20 can also be) thank you!
It is necessary to calculate by the formula

12×4.84.（3.2×1.5+2.5）÷1.6 （2）3.2×（1.5+2.5）÷1.65.6-1.6÷4= 5.38+7.85-5.37=6.7.2÷0.8-1.2×5= 6-1.19×3-0.43=7.6.5×（4.8-1.2×4）= 0.68×1.9+0.32×1.98.10.15-10.75×0.4-5.79.5.8×（3.87-0.13...

The bottom radius of a cylinder is 4cm and its height is 8cm. Find its volume and surface area

Volume = bottom area × height
=4×4×3.14×8
Surface area = bottom area × 2 + side area
=4×4×3.14×2+2×4×3.14×8

How is the constant and impossible speed of light deduced?
Don't say anything else, just say how Einstein deduced these two conclusions!
How Einstein came to the conclusion that the speed of light is constant
How Einstein came to the conclusion that the speed of light cannot be exceeded
Einstein's relativistic mass formula
m=m0/(1-v^2/c^2)^0.5
M is equal to M 0 minus V squared by C squared
M0 is the static mass, M is the moving mass, C is the speed of light, and V is the moving speed of the object. From this formula, we can see that the larger V is, the smaller the denominator is, the larger m is
So how does this thing work out?

You just understand the opposite. The argument of "constant speed of light" is not derived by him, but observed by experiment
At the beginning, Michelson and Murray designed an accurate instrument, the interferometer, which can measure the tiny change of the speed of light. Because the earth moves relative to the sun, measuring the speed of light of the sun in different directions should be different. The accuracy of the interferometer is enough to measure this difference. However, to their disappointment, the experimental results show that the speed of light is constant
So Einstein took the experimental result of "no matter how the relative light source moves, the speed of light always remains the same" as the basis of deduction, and derived a series of strange conclusions, such as: length shortening, time slowing down, mass increasing and so on, namely special relativity
According to the formula, the greater the speed, the greater the mass. When the infinity approaches the speed of light, the mass tends to infinity. Therefore, it is more and more difficult to accelerate it, It takes an infinite force to accelerate it again. So in dynamics, you can't accelerate an object to the speed of light

Two force balance physics problems
The total weight of a parachute jumper and parachute is 700n. In order to shorten the landing time, the parachute does not open at the initial stage and the speed increases continuously. The resistance of the parachute jumper (including parachute) is () the total gravity of the parachute and the parachute. After opening the parachute for a period of time, the parachute drops at a constant speed of 5m per second. At this time, the resistance of the parachute jumper (including parachute) is () the total gravity of the parachute and the parachute, The speed of the athlete decreases continuously, the resistance of the athlete (including the parachute) and the total gravity of him and the parachute
The reason!!!!

Less than
be equal to
greater than
According to the common sense analysis all right, who strong who lead, thank you

As shown in the figure below, the side length of square a and B is 5.2 cm, and one vertex of square a is located in the center of square B. calculate the area of the shadow part

Because the vertex of square a is always at the midpoint of B, no matter how you move it, the area is the same as the shadow part. Move to the two vertices of B to form a triangle, and you will find that the shadow part is a quarter of B. the formula is: 5.2 times 5.2, then divide by 2, and then divide by 2, equal to 6.76 square centimeter