Xiao Gang bought a lamp for the study, and there are two kinds of lights available for purchase, one

Xiao Gang bought a lamp for the study, and there are two kinds of lamps available for purchase, one of which is 9W (that is, an energy-saving lamp, priced at 49 yuan; The other is 40W (i.e., an incandescent lamp, priced at 18 yuan, assuming that the brightness of the two lamps is the same, the service life can reach 2800h, and it is known that the electricity price of Xiaogang's home is yuan per kilowatt hour.

Q: If the lighting time is 3000 hours, then you must choose to choose two lights at the same time, please give the design the most expensive lighting plan.

If the time of the energy-saving lamp is x, the time of the white lamp is 3000-x. The total cost is yy=49+18+. 5+。5

67+ because x<=2800

So the cost is the least, then x=2800.

Even if the time of using energy-saving lamps is 2800 hours and the time of white lights is 200 hours, the total cost is the least, is: 127-0

1) The cost of energy-saving lamps is S1, the cost of incandescent lamps is S2, and the lighting time is Xs1

s2 makes s1>s2, and the solution is x<2000 In the same way, the cost of energy-saving lamps is low when s1x<2000.

2) One energy saving and one incandescent, energy saving takes 2800 hours, and then incandescent is used.

Solution: (1) Assuming that the lighting time is x hours, the cost of using the two lamps is the same, according to the topic

49+, solution x=2000, answer: when the lighting time is 2000 hours, the cost of the two lights is the same;

When the lighting time is less than 2000 hours, the cost of using incandescent lamps is low When the lighting time is more than 2000 hours, the cost of using energy-saving lamps is low;

2) Discuss the following three situations:

If two energy-saving lamps are selected, the cost is 98+ yuan;

If two incandescent lamps are selected, the cost is 36+ yuan;

If one energy-saving lamp and one incandescent lamp are selected, it can be seen from (2) that when the lighting time is 2000 hours, the cost of using energy-saving lamps is lower than that of incandescent lamps, so when energy-saving lamps are used for 2800 hours, the cost is the lowest

The cost is 67+ RMB

To sum up, one lamp should be selected for each, and the cost is the lowest when the energy-saving lamp is used for 2800 hours and the incandescent lamp is used for 200 hours

1) The cost of setting up energy-saving lamps is 41, the cost of incandescent lamps is 42, the lighting time is xling s1>s2, and the solution is x<2000 Similarly, the cost of energy-saving lamps is low when s1x<2000.

2) One energy saving and one incandescent, energy saving 2800 hours, and then use incandescent lamps.

Let me help you add: Xiao Gang bought a lamp for the study. Two types of lamps are available for purchase, one of which is a 9-watt (i.e. kilowatt) energy-saving lamp priced at 49 units; The other is 40 watts (5 pcs).

1 Set the illumination time to x, expressed as an algebraic expression containing x.

The cost of using an energy-saving lamp is -49+ yuan.

How much does it cost to use an incandescent lamp – 5+? Yuan.

2. Xiaogang wants to buy one of these two lights.

1 When the illumination time x = - h, it costs as much to use both lamps (the equation for x is Solution: Solve 49+

Missing data. How much electricity per kilowatt is not said and cannot be calculated.

Middle School Math? I miss it.

1.Energy-saving lamp cost = 49+, incandescent lamp cost = 18+

2(1).Because, when 49+, it costs as much to use both lights.

That is, when x = 2000h, it costs the same amount to use both lamps 2 (2).From the above formula. Energy-saving lamps are used for lighting time of more than 2000 hours, and incandescent lamps are used for lighting time of less than 2000 hours.

2(3).Upstairs, the process doesn't seem right.

Set incandescent lamps for a hour and energy-saving lamps for 3000-a hours. The fee is s, and when a=0, s=18*2+

When a=3000, s=49*2+

When 20<=a<=2800, s=49+18+a*, that is, when a=20, s has a minimum value.

1. The cost of energy-saving lamps = 49+; Incandescent lamp cost +, x = 2000 hours.

2-2. Energy-saving lamps should be selected for lighting time of more than 2000 hours, otherwise they are incandescent lamps 2-3, and 1 should be selected each. If you choose 2 incandescent lamps, the cost = 2*18+; If you choose 2 energy-saving lamps, the cost = 2 * 49 +. 96；If 1 incandescent lamp and 1 energy-saving lamp are selected, the cost = 49 + 18 +

Solution: (1) Assuming that the lighting time is x hours, the cost of using the two lamps is the same, according to the topic

49+, solution x=2000, answer: when the lighting time is 2000 hours, the cost of the two lights is the same;

When the lighting time is less than 2000 hours, the cost of using incandescent lamps is low When the lighting time is more than 2000 hours, the cost of using energy-saving lamps is low;

2) Discuss the following three situations:

If two energy-saving lamps are selected, the cost is 98+ yuan;

If two incandescent lamps are selected, the cost is 36+ yuan;

If one energy-saving lamp and one incandescent lamp are selected, it can be seen from (2) that when the lighting time is 2000 hours, the cost of using energy-saving lamps is lower than that of incandescent lamps, so when energy-saving lamps are used for 2800 hours, the cost is the lowest

The cost is 67+ RMB

To sum up, one lamp should be selected for each, and the cost is the lowest when the energy-saving lamp is used for 2800 hours and the incandescent lamp is used for 200 hours

A 9-watt energy-saving lamp is definitely not as bright as a 40-watt incandescent lamp. Buy energy-saving lamps, safety first. The incandescent lamp is too hot for a long time.

Solution: (1) Assuming that the lighting time is x hours, the cost of using the two lamps is the same, according to the topic

49+, solution x=2000, answer: when the lighting time is 2000 hours, the cost of the two lights is the same;

When the lighting time is less than 2000 hours, the cost of using incandescent lamps is low When the lighting time is more than 2000 hours, the cost of using energy-saving lamps is low;

2) Discuss the following three situations:

If two energy-saving lamps are selected, the cost is 98+ yuan;

If two incandescent lamps are selected, the cost is 36+ yuan;

If one energy-saving lamp and one incandescent lamp are selected, it can be seen from (2) that when the lighting time is 2000 hours, the cost of using energy-saving lamps is lower than that of incandescent lamps, so when energy-saving lamps are used for 2800 hours, the cost is the lowest

The cost is 67+ RMB

To sum up, one lamp should be selected for each, and the cost is the lowest when the energy-saving lamp is used for 2800 hours and the incandescent lamp is used for 200 hours

Energy-saving lamp: yuan).

Incandescent lamp: yuan).

Choosing energy-saving lamps can save money.

I don't accept this post.

Why is there no follow-up?

First, the whitish is not dazzling. Second, the lighting is soft but shining.

Under the premise of the same power, the brightness of the tri-color energy-saving lamp is 5-6 times that of the incandescent lamp, of course, it saves electricity and money. According to the calculation of a 40-watt incandescent lamp illumination for 5 hours a day, if each kilowatt-hour of electricity is calculated at 5 jiao and 5 cents (the electricity cost varies from place to place), the annual electricity consumption is 73 kilowatt-hours, and the electricity cost is 40 5 365 1000 yuan, plus two light bulbs for 1 yuan, and the annual cost is yuan. If you use high-quality energy-saving lamps, you only need a 9-watt three-color energy-saving lamp, and the annual electricity consumption is only kilowatt-hours, and the electricity bill is 9 5 365 1000 yuan, plus 10 yuan of the energy-saving lamp itself, and the annual cost is only one yuan.

In the case of the same illumination, a 9-watt energy-saving lamp can save 66 yuan per household throughout the year, based on an average of 3 lamps in an ordinary family.

The state advocates energy conservation and emission reduction, so you can buy energy-saving lamps.

I guess this is a physics question, and the physics teacher who came up with this question is a stupid ......You go to school and ask him if you drank too much when you took the question.

If you don't specify such an important condition, we're a fart!

Children, just make an equation and calculate it. x is the time, and the rest is solved by itself.

I'm thinking about it, and I don't feel the same way as you.

Answer: 1) The cost of energy-saving lamps and incandescent lamps is Y1 and Y2 respectively

y1=y2=2) When the two lights cost the same, y1-y2=0, i.e.:

Solve the equation and get: x=2000 (hours).

That is, when the lighting time is 2000, the cost of using both lamps is the same.

When x = 1500 hours, the cost of using incandescent lamps is low; When x=2500 hours, the cost of using energy-saving lamps is low;

By conjecture: when the lighting time is less than 2000 hours, the cost of using incandescent lamps is low; When the lighting time is 2000 hours, the cost of using energy-saving lamps is low;

3) Xiao Ming wants to buy two of the two lights, the precision lighting time is 3000 hours, and the service life of each lamp is 2800 hours, then the following plan can be used with the lowest cost:

2800 hours for 1 energy-saving lamp and 200 hours for 1 incandescent lamp: y=yuan.

The reason can be expressed in an equation:

The total cost is y, the time used for energy-saving lamps is x1, and the time used for incandescent lamps is x2, and the system of equations is as follows:

y=(x1+x2=3000

0<=x1,x2<=2800

Solve the system of equations and get: y=

Therefore, when x1 is the largest, y is the smallest, that is, the longer the energy-saving lamp is used, the lower the cost.

Therefore, energy-saving lamps are used until the end of their life for 2800 hours.

Solution: (1) The cost of using an energy-saving lamp is (78+ yuan, and the cost of using an incandescent lamp is (26+ yuan;

2) From the meaning of the question, 78+ is obtained, and the solution is x=2000, so when the lighting time is 2000 hours, the cost of both lights is the same

When x = 1500 hours, the cost of energy-saving lamps is 78 + yuan, and the cost of an incandescent lamp is 26 + yuan, so when the lighting time is equal to 1500 hours, the cost of using incandescent lamps is low.

When x = 2500 hours, the cost of energy-saving lamps is 78+ yuan, and the cost of incandescent lamps is 26+ yuan, so when the lighting time is equal to 2500 hours, the cost of energy-saving lamps is low

When the lighting time is less than 2000 hours, the cost of using incandescent lamps is low; When the lighting time is greater than 2000 hours, the cost of using energy-saving lamps is low;

3) Discuss the following three situations:

If two energy-saving lamps are selected, the cost is 78 2+ yuan;

If two silver incandescent lamps are selected, the rental cost of the model is 26 2+ yuan;

If one energy-saving lamp and one incandescent lamp are selected, it can be seen from (2) that when the lighting time is 2000 hours, the cost of using energy-saving lamps is lower than that of incandescent lamps, so when energy-saving lamps are used for 2800 hours, the cost is the lowest

The cost is 78+ RMB

To sum up, one lamp should be selected for each, and the cost is the lowest when the energy-saving lamp is used for 2800 hours and the incandescent lamp is used for 200 hours

Let the cost of using energy-saving lamps be $A, and the cost of using incandescent lamps will be $B

Illumination time is x hours in the case of:

a=49+9*x*

b=18+49*x*

1): If the cost of using two lamps is the same as if the lighting time is x hours, there are:

a=b is 49+9*x*, and the solution is:

x=1550, that is, the cost of using two lamps is the same as when the bright time is 1550 hours;

2): When B loses 1550, and it is known that the service life of the two lamps is 2800 hours, then there is a time when the lighting is in the range of 15503) There is the calculation result in (2) that the cost of using incandescent lamps is low when the lighting time is in the range of 0 1550 hours, and the cost of using energy-saving lamps is low when the lighting time is in the range of 1550 2800 hours;

In the case of a total lighting time of 3000 hours and a service life of 2800 hours for both lamps, you can buy two lamps: an incandescent lamp and an energy-saving lamp, first use incandescent lamps for 200 hours, and then use energy-saving lamps for 2800 hours, so that the total cost can be the lowest is: yuan.

1) Energy-saving bulb cost = 49+

Incandescent Lamp Fee = 18+

When solving x=1550 small good suspicion.

2.The lighting time is 0-1550 hours, the cost of using incandescent lamps is low, and the lighting time of search difference is 1550-2800 hours, and the cost of using energy-saving lamps is low.

3) Lowest cost plan world sock leather:

Buy an energy-saving lamp and light it for 2800 hours, and then buy an incandescent lamp and light it for the remaining 200 hours, and the total cost is RMB.

I've asked this question n times...

1. The cost of the energy lamp = x 2800 * 49 The cost of incandescent lamp = x 2800 * 18

2. The cost of using an energy-saving lamp until it is used up.

Yuan. The cost of using an incandescent lamp until the base is used up.

74 yuan. So, of course, choose energy-saving lamps that save money.