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It is known that the sum of the first n terms of the arithmetic sequence an is Sn, and satisfies A2 + A4 = 14, S7 = 70
The acceleration of a car moving at 12m / s after emergency braking is 5m / S ^ 2. Calculate (1) the speed at the end of 2S after braking (2) the displacement within 6S after braking
1、Vt-V0=at
A is opposite to V, a = - 5
0-12=-5*t
t=2.4s
stop it
Velocity at the end of 2S V2 = V0 + at = 12-5 * 2 = 2m / S
(2) The displacement within 6 seconds after braking is the displacement of 2.4 seconds
Vt^2-V0^2=2as
0-12*12=-2*5*s
s=14.4m
Xiao Li and her father compete in the 1200 meter walking race. Her father's speed is 1.5 times that of Xiao Li. Xiao Li takes 5 minutes more than her father to finish the race. She asks Xiao Li how many meters she and her father walk each minute
Suppose Xiao Li walks x meters per minute, 1200 / 1.5x = (1200 / x) - 5, and the solution is x = 80, then Xiao Li's speed is 80 and his father's speed is 120
1. Xiaolan is going to use 30 yuan to buy pens and notebooks. It is known that a pen costs 4 yuan and a notebook costs 3 yuan. If she has bought 8 pens and notebooks in total, how many plans does she have? (Note: 30 yuan is not enough)
2. Xiaoming's family is considering traveling this summer vacation. He contacted two travel agencies. The charge standard of travel agency a is: one parent buys a full ticket, and the rest of the members buy half price tickets. The charge standard of travel agency B is: family travel is based on group tickets, calculated by 2 / 3 of the ticket price. It is known that the original price of the two travel agencies is the same, Xiaoming found that a travel agency is more favorable after correct calculation. Please judge the number of Xiaoming family
3. The purchase price of apple is 2 yuan per kilogram. It is estimated that 20% of the apple will be consumed normally in the sales. How much can the seller set the price at least to avoid losing money?
4. In order to speed up the modernization of teaching methods, a school plans to purchase a batch of computers. It is known that the quotation of company a is 5800 yuan, and the preferential condition is to buy more than 10 computers, then 70% of the quotation will be calculated from the 11th one; the quotation of company B is 5800 yuan per computer, and the preferential condition is 85% of the quotation, Under the premise of the same brand, quality and after-sales service, how do you choose? Please explain the reason
5. The solution X of the equation 5x-2m = - 4-x satisfies 2
I will answer question 2
There are x family members and the original price of travel agency is y yuan per person
Y + 0.5y (x-1) < 3 / 2XY (two thirds XY)
0.5y + 2 / XY (half XY) < 3 / 2XY
0.5Y＜6\XY
X＞3
A: there are more than three people in Xiaoming's family
On the number axis, the distance to the point corresponding to - 1 is equal to the number corresponding to the point with root 3?
[- 1 - (radical 3)] or [- 1 + (radical 3)]
Solution of ternary linear fractional equations
(1/x+1/y)×6=1
(1/y+1/z)×10=1
(1/x+1/z)×5=2/3
Please write down the process, thanks
1 / x + 1 / y = 1 / 6, 1 / y + 1 / z = 1 / 10, 1 / Z + 1 / x = 2 / 15, 1 / x + 1 / y + 1 / z = 2 / 5, 1 / x = 3 / 10, x = 10 / 3, 1 / y = 4 / 15, y = 15 / 4, 1 / z = 7 / 30, z = 30 / 7
In the equal ratio sequence {an} with common ratio 2, Sn is the sum of the first n terms. If s99 = 56, then A3 + A6 + A9 + +The value of A99 is ()
A. 4B. 8C. 16D. 32
In {an} which has a common ratio of 2, the sequence {a3n} is an equal ratio sequence with a common ratio of 8. Let s = A3 + A6 + A9 + +Then s = A3 (1-833) 1-8 = A1 · 4 · (1-299) - 7, ① ∵ s99 = 56, ∵ A1 (1-299) 1-2 = - A1 (1-299) = 56, ② comparing the two formulas, s56 = 47 and S = 47 × 56 = 32 are obtained
3 / 4 square decimeter = () square meter?
3 / 4 square decimeter = (0.0075) square meter
In an earthquake relief, a city organized 20 vehicles to transport three kinds of relief materials, including food, medicine and daily necessities, to the resettlement area. According to the plan, all 20 vehicles should be transported, and each vehicle can only carry one kind of relief materials and must be filled up Type of goods and materials: food, drugs and daily necessities: Freight (RMB) 120 160 100 (1) how many tons of disaster relief materials are loaded by 20 vehicles? (2) How much is the total cost of shipping this batch of disaster relief materials?
(1) There are (20-x-y) vehicles carrying daily necessities, so the disaster relief materials loaded by 20 vehicles = 6x + 5Y + 4 (20-x-y) = 6x + 5Y + 80-4x-4y = 2x + y + 80 (tons); (2) total cost = 120 × 6x + 160 × 5Y + 100 × 4 (20-x-y) = 720x + 800Y + 8000-400x-400y = 320x + 400Y +
How many cubic meters is a ton of stone
Different density, different quality
Granite: 2.63 ~ 3.3, syenite: 2.3.3, diorite: 2.3.3,
Porphyry: 2.8, andesite: 2.3.3, diabase: 2.7, 2.9,
Rhyolite: 2.3.3, granite gneiss: 2.2.9, gneiss: 2.2.8,
Quartzite: 2.61, 2.3.0, marble: 2.3.3, phyllite (slate): 2.3.3,
Tuff: 2.3.3, volcanic breccia (volcanic agglomerate): 2.3.3,
For example, granite: density 3.3g/cm ^ 3, 1t = 1000kg
V ＝m/ρ=1000000/3.3=303030.3cm^3
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